My bus is solar so I think I can share a bit with you. I'm still converting but I've had solar connected now for months and working great. I made some mistakes and did a lot of homework to get to this point.
I think I can sum up the most important stuff:
Shadows turn off solar power! Really! If you look at a solar panel it is made up of a bunch of squares (cells) all connected in series (there are some new panels that are series/parallel but most are not). Those cells can be thought of as light activated switches... now stay with me here. When the sun shines on those cells they all turn on like a bunch of switches in series. But if you take two playing cards and cover up one of those cells you turn off that switch and the whole panel essentially TURNS OFF! You will still measure a small bit of current coming from the panel but not much. So first lesson is... placement is important. Anything taller than your panel that can cast a shadow across ANY cells can have a significant impact on your system! I can watch current go up and down with the thinnest of clouds passing overhead. A leaf on your panel will have an impact on output. Im not that worried about a leaf but if I need to recharge in the fall and leaves have fallen on my panels I'm gonna move the bus and clean them off. Installers screw this up all the time on big rv' with air conditioners and vents and dish antennas. It's crazy. Watch out for shadows.
Wire size. Low voltage with high current requires large wire sizes to prevent significant loss of performance. High voltage low current can use smaller wire gage. If you put panels up in series then the system voltage is the sum of each of the panels in series. If they are in parallel the the system voltage will be the same as one of the panels. Learn about minimum wire gage with respect to voltage and current and then go one size larger or more. Don't loose all of your power through the wires!
MPPT charge controller or standard charge controller? If your solar system voltage closely matches your battery voltage then you don't really need MPPT. But keep in mind... Solar won't charge your batteries until your solar array voltage rises above your battery bank voltage. You need 13 volts and more to properly charge a 12volt battery bank. In the early morning when the sun is low in the sky the voltage of your array may be significantly lower than later in the day. If you have an array that outputs 16-18 volts during the day, it may only output 10-12 in the early morning. That's not charging your 12 volt bank. In contrast, I have two 48 volt panels in parallel charging my 12volt bank. In the early morning they may only output 18 volts but that's still enough to start charging the batteries! And because my solar array voltage does NOT closely match my battery bank voltage I require an MPPT charge controller. The MPPT controller is essentially a DC to DC converter that drops the incoming solar voltage to a usable charge voltage for my battery bank. I have two "house size" solar panels on my bus for a total of about 480 watts. I went this way because house panels are generally less expensive per watt than rv (lower voltage) panels. Way less expensive. And the higher voltage panels start charging my batteries earlier in the day and keep charging later into the evening. I recommend higher voltage systems in concert with a decent MPPT charge controller. Be careful to choose a controller that will handle the voltage and current coming from your array.
Batteries. 6 volt golf cart style batteries are old school and still hard to beat. They're rugged and can take some punishment and keep going long after others fail. That said... you would be wise to limit deep discharges on your battery bank. If you regularly discharge your bank to half charge (half of the total bank amp/hr capacity) your batteries may not last but a couple of years. But if you only discharge to 70% or so they might last ten years! Two things kill batteries... Hard or deep discharges and improper charging (most of the time it's because they don't receive a full charge). Batteries should be topped off regularly and it takes higher voltages than most chargers attain. Learn about proper charging of batteries and purchase a charge controller that allows you to adjust charge voltages and time.
Oh... and there is another reason batteries fail... Lack of electrolyte. Batteries need to be watered. If the water drops below the tops of the cells the batteries can be damaged. If you can't get to the batteries easily to top them off monthly the consider getting a watering system that will make it easier. Then set a monthly reminder on your cell phone.
Battery monitor (fuel gage). This is a must have. If you don't know how much power is left in your batteries then your always guessing their state of charge. You're gonna spend a couple hundred dollars on this monitor. Anything less probably won't do. Get past the expense... you need it. I also have a cheap gage that was a $30 accessory for my charge controller. It's crap. To properly read the state of charge on your batteries you must connect the monitor and current shunt (that comes with the monitor) directly to the battery bank, not some distance away. The gage is reading current and voltage. A voltage drop across wiring of 1/10th of a volt can greatly affect the battery monitor readings.
Lastly I suggest getting a Kill-A-Watt meter. You plug in appliances you plan to use into the meter to measure their wattage used over time. Name-plate amps and watts rarely give you an accurate representation of actual watts used by the appliance. Often the watts used is considerably less. Using this meter will help you get a feel for the wattage requirements of your appliances and help you determine what you need from solar and batteries.
Just a little more... Covering your bus with panels to charge a four battery bank is likely a waste of money. Adding a ton of batteries is equally wasteful. If you install your solar panels away from shadows, use heavy appropriate gage wire, good deep-cell batteries, a properly matched charge controller and use a good battery "fuel gage" to monitor usage you will get the most out of your system.
I hope this was helpful! A couple of pictures below: