Just basic real life info for those who think they don't really need much insulation.
It wasn't a skoolie...
We have wintered several years in a vintage Sticks-n-Staples 22 ft Class C. My daughter currently full times in it. The roof, walls & floor are all 2" blue foam. I know because we tore apart the back section to rebuild (lousy roof rack & ladder set up leaked for years apparently). The old Suburban furnace is a fairly economical one. It sucked a 20 lb LP tank every 2 weeks (also cooked on LP). We ran one of our old 100 pound tanks in NC. We also had an electric heater going as well at the same time. The Class C has wintered in Elizabethton TN, Franklin NC, Cordele GA, Socorro NM (similar temps to Franklin & Elizabethton) and Corpus Christi TX (similar temps to Cordele). Good learning experience. We have learned you can never have too much insulation. Ditto for summer heat. Lots of cold comes up from the floor so you can't forget about the floor. The heat off the summer interstates cooked the contents of our uninsulated tanks on the Class C. And our "cold" showers were so hot, we didn't kick the water heater on. Insulation is needed for hot & cold temps. And you can not have "too much" insulation.
We have bounced all over the place trying to balance budget, availability and R-Value. We have settled on, then discarded so many options. The ones I am listing here may get changed in a few months. Sometimes you can over think a simple thing. At some point we will just say enough, time's wasting away, and start insulating. Maybe we'll put up some Reflectix heat barrier first....
We are going to pack as much insulation under the floor as we can afford (rigid foam sheathing with canned spray foam filling in the "spaces"). We think 6 " will do a decent job. The roof seems to be insulated pretty well on our bus. But if we decide it's needed, we would add the insulation to the roof top. I know of a super insulated roof
that was put on the outside of a coach due to low head room. But it's snowed a few times here in Roswell and the snow piled on the roof while we ran heat inside. The uninsulated floor was terribly cold though. A heated mattress pad on the bed is wonderful. For winter we put a sleeping bag slid into a duvet cover on the bed. It's like "personal" insulation.
Rivets in the side walls transfer cold (and heat) pretty bad. They will get covered with 1" foam over the original walls. All the screws in the furring strips will be off set to create thermal breaks. thermal breaks are very important. It doesn't matter if you have 6" of insulation in your roof/wall if you have a source for the cold (or heat) to pass thru the insulation. Or if you sprayed your walls & ceiling with foam then planted a screw into the metal framing tube, then you have probably created a heat sink since the framing tube has exterior rivets tapped into the tube making a thermal connection. I've heard some lovely ice stalactites can form in the winter time due to a rivet or screw heat sink.
Reflectix, the shiny metallic bubble wrap looking stuff, is a heat barrier, not really an insulation. If you get the one with the single shiny side, the shiny side should face to the exterior (all shiny heat barriers should face away from the living area). It also needs a thin (1/8") air gap to work right. Although I have installed it with no air gap on a road cover/roof of a popup camper it it worked quite well. Reflecitx is very handy to cover your single pane windows with along with the aluminum frames the window are in. Aluminum is a terrific conductor of heat and cold. If the idea of living in a dark windowless cave all winter makes you depressed, then you will be happy to hear that plain clear bubble wrap (the packaging kind)does a wonderful job of insulating windows. Almost as good as Reflectix, yet lets light in. While you may want to cover your big windshield with Reflectix, you can still put some clear bubble wrap over some of your smaller windows (making sure to cover that pesky aluminum frame) to let in some much needed light.
While not an insulation, a reflective roof coating goes a long way towards keeping the heat out plus it coats and seals rivets, bolts and screws from thermal conductivity. In other words, it creates a thermal break. And does a wonderful job of sealing any leaks too. We used Henry's 287 Solarflex
on our roof. For a 40 ft bus, roll 5 gallons on in about 3 coats (first seal seams & leaks with elastometric caulk
The best way we have found to beat the cold is to go south of 35°Latitude. The closer to that point the colder aspects of winter you will have.Now there are some micro climates there that do mess with that statement. Chattanooga is at 35.04° and the winters there were milder than the winters in Socorro which is at 34.06°. Roswell at 33.40° has even milder temps than Socorro. Chattanooga & Roswell are both on water which keeps them warmer in the winter and cooler in the summer. South of 30° is some pretty mild winters. Far enough north that you aren't right on the coast or in FL paying higher site rent but far enough south that you rarely get freezing tempos for more than one or two nights in a row (which is still enough to freeze up a crappy Valterra gate valve). I've got two more winters to suffer thru before we can go farther south (30° Latitude). For summer heat, your best bet is to go up in ALTITUDE!
The coming winter won't be as bad as last winter for us. We will have the heat exchanger set up and insulation on the walls and under the floor (with the tanks heated/insulated). We will also have an LP heater in the bathroom to boost the heat there for showers & in case the power goes out on us... again. Something that needs to be planned for. Since we started full timing again (2006), we have not been without power or water (frozen/broken city pipes) for more than 1 day. We've been lucky too. Albuquerque lost power for over a week due to a winter storm. I also plan on making a couple of MEN's heat grabbers
to collect some daytime heat from the plentiful NM winter sun.
Of course that may all be overkill because "it never get's that cold here" and "it rarely snows much here" is told to use everywhere we go.... Yep, it snows so little & so seldom in Socorro, that they "didn't" close down I-25 (which seems to only take a few inches)for two days.
This is what it did just before we left to go to Roswell. This was the 2nd snow storm that kept us from leaving as planned.
By the time the snow stopped, there was 18" laying... It's rarely snows in Socorro. And it "rarely" snows in Roswell!