Hi,
You are concerned about your animals, I think, as a first thing.
A) If money is supertight but you can swing it -- because it is a part of every other option I'm thinking of working well, get 4 more of your 12V 100AH LiDFePo4 batteries (or 1 more, more is better up to 8kWh ~ 10kWh storage) and two 400W 12V solar panels ( or just a handful more of 100W again until you are past 12kW you don't have "extra" panels), and get a dehumidifier. SanTan Solar I can recommend for panels, their batteries are not that great a deal. NoName 12V 100AH LiFePo4 can be seen on Amazon for $100~110ea., really good ones for $130~$160. Altogether this will be about $1.1k ~ $1.5k, and you need the power to run the A/C and humidifier at night --
you will make back what you put into solar collection and storage by not running the generator as much or at all for weeks at a time,
Even with only minimal insulation, if you put that together with blocking off half the bus during the day with a blanket, I really believe the cooled half will be tolerable in soggy sunny Florida.
B ) You aren't moving into a tent while you gut the bus, so you aren't gutting the bus. This will have minimal further cost. Mostly this is effort plastic sheeting and tape. < $500.00.
If you have reflectix on the windows, then you are already not worried about seeing out of the windows. Clean the windows to water clear if you can, as much as you can. Have the least crud/dust on the glass to intercept light and heat up. Wipe the reflectix dust free on the shiny side and then put it back in the windows. Tape plastic sheeting all around the borders of the windows to zero air infiltration from them.
Keep one unsealed.
Get a hair dryer (any small blower). I have no idea if a cigar is cheaper than a pack of cigarettes, but get whichever is cheaper. Take the unsealed window and rig the blower (on cool for hair dryer) through cardboard and plastic, pointing in and sealed up. You are trying to inflate the bus. Take the lit smoking product and pass it over all fittings, apertures, corners, seals, the dash, etc. You are looking for cracks to tape over. It might be so leaky you have trouble isolating any, I have no way to know. If you get to the point you can't secure the blower with tape because you
are inflating the bus, then you might have tightened it up enough to worry about oxygen depletion -- then you might need to keep a vent open/window cracked. I can't believe you'll get there, too much deliberate ventilation and ports in the dash/firewall.
Seal up that last window like the others.
In addition to a regular window style A/C, get and run a dehumidifer. You will not get away I think without running the generator every evening as late as the neighbors can stand, because the battery storage to avoid it is not there. The point is low humidity air at 85deg can be stood by most people and animals with a fan, 75deg at 90% humidity is horrible.
Silica gel dehumidifiers are not the way to go unless you can use a lot and can safely ( for them ) heat the silica outside to dry it back out). Doing that would become a daily or near daily chore. If you don't reuse the silica, dry silica bead costs will eat you alive -- but you don't want to be drying them in the bus because that puts the moisture and heat from drying them back into the bus. The little solid state dehumidiers (or say they are Peltier) are quiet and cheap, but also low capacity and put a lot of heat into the bus for what they do. You are looking for a single room refrigeration cycle dehumidifier with compressor and fan.
C) You are going to move into a tent while you gut the bus.
Wow, do you have options, like hella lotta options.
$900 gets a 600 board ft spray foam kit from Amazon that will probably get R6 at least while zeroing air infiltration wherever it goes. With a wire wheel you can probably pare it back to where you can put the original interior metal back, and you need the wire wheel to clean up all rust and loose paint before spraying. Also before spraying, cover any rust with rust converter. You have a lot of area in the front windows you can not cover and it is and will be single glass sheets, there's not a lot you can do with that. With 20' you can't really spare the living area either. This will get you the best performance out of any given combo of A/C and dehumidifier. This plus incidentals (like a breather and tyvek suit, so you can install the foam safely) probably could be done for <$1,500. That is $1,500 in addition to more panels, batteries, and the dehumidifier.
This is a potentially suitable spray foam option (I have not used it) with less coverage and more variable reviews towards customer satisfaction -- but, less than half the cost for way more than half the coverage.
The chief advantage of any spray foam of closed cell type is the 100% sealing from air infiltration and no volume inside the metal to trap water vapor, which you get in addition to R6~7 per inch of depth.
Then you have all the other options.
Rigid foam boards, fiberglass, natural options like wool, and reflective materials.
I think none of the last three are good for your application because of the difficulty of keeping a vapor barrier of plastic intact while installing them. Any place there is a leak you will get water condensing and being trapped. There will be mold and rust. Frankly, "natural options" will be food for mold when wet.
Rigid foam with great stuff gap sealer is an option, probably comes to a middle of the other foam options for cost, and -- the foam board manufacturer has done the job of creating the foam correctly. For either other spray foam option it is on you to have the temperature right (still required for gap sealer but larger allowed range) and prepare the surface for foam adhesion and to mask off any areas where any overspray must not be allowed to land. If you do rigid foam and don't seal it up, then you are back to some degree of water condensation inside the metal envelope of the bus -- but the foam board itself will not absorb water and it's outer surface will not condense water much if at all.
I am predicating these suggestions on the idea your generator can not be run at night much or people will b***h and make you move, and, you aren't getting gas for free. Most of these will almost certainly save $1000plus in gas the first year, and then keep on doing that for years. As is (400W of solar) you will need to run the generator some of the time during the day, so . . . Adding a 400W panel and a few batteries while definitely getting a dehumidifier to go with the A/C and sealing up every air leak you can is a first step.
If the A/C you have is all the time running water then it may be doing a good job of dehumidifying air already, but, if it starts to ice up then it
needs dedicated dehumidifying help.
I hope your future experience leaves you feeling I've covered options well.
TL/DR. You do not need 20 solar panels, but, you need more panels period, like 2X, 3X of what you have, and 2X storage. Probably you need a dehumidifier for Florida and to seal up every air leak you can. You have reflectix for all windows, right, and LED lighting? The expenditure I am thinking of will pay for itself beginning on completion and in 1.5 ~ 3 years, and likely means you may get away with not running the generator for weeks at a time.
For that 3X panels to work, I am counting on lowered humidity letting you get away with not running the A/C nearly as much. Having the A/C run at between 60% ~ 66% duty cycle 24/7 and you are back to always needing the generator, or, you need that 3500W of solar. Almost all 12V panels you can parallel without worrying much about differences in wattage, so you can always add panels a bit at a time -- key thing to that is keeping the Vmp as close as possible for all panels.
The present value of avoided future cost for gasoline, minus the cost of even the most expensive option, is more than twice the cost of the most expensive option. Any of it is a good use of your money.
