Your RV should be using 35 amp hours per day to run the propane, CO detectors and the refrigerator. That is about what one 120 watt solar panel will make up in one day. Of course you probably also want to run a small inverter to power the telescope while it is tracing whatever star you are looking at?
You might want a 300 watt 12 to 120 VAC inverter that plugs directly into a cigarette lighter. This will also charge your laptop, and other small devices.
If you already have one group 27 battery, then another will supply about 80 AH each or 160 total. If you also run a small generator for a couple of hours on the second day, you will put back around 25 AH per hour, and put back enough for another night. But generators are typically heavy, noisy (compared to the silent solar panels) and expensive (compared to a solar panel). Also the generator if you only use it twice each summer, then it sits for 9 months, it will be really difficult to start next time.
Solar has come down drastically in price. My 1994 set of panels where 90 watts, with a 15 amp controller, brackets, wiring instructions (this was before google) for $750. Back then you could rent a 4 BR house for that much each month! Now you can get a 140 watt panel for $229.
SunElec.comYou will want a 12 volt nominal panel (with 20 - 21 volts open circuit voltage). And a cheap PWM controller (I bought one for $13 that is rated at 20 amps). Mounts can be made from 6" long 2: angle aluminum (home depot) and wiring is grey Romex that is UV rated, and can be run underground or out in the rain.
Run the wires down the refrigerator vent, and to the controller, to the battery. You could also run it to your converter/12 volt battery box and wire it to a fuse there, to saving wiring costs, and make it easier on you.
IT should take you less than 4 hours to install the solar system. The wiring is really simple, as there is +12 volt wire, and - 12 volt wire. Do not connect both wires to the same terminal, and you have it right!
Buy a tube of rubber roof sealant, and put some on each mount between the roof and mount. Once it is dry, it will hold the mount to the roof, and 3 #10 screws into the roofing will also help. Put sealant over each screw once installed. 1/4" bolt into each corner of the solar panels, and that will hold the panel about 1" above the roof, so it stays cooler, and works better.
Now you will be ready to dry camp for years. I figure that my $3,000 system (with large inverter, 415 rated watts of panels, SB 50 MPPT controller and $375 Trimetric meter that measures the amp hours leaving the battery very accurately to monitor how much power is used minute by minute) has saved me well over $3000 in the first 10 years. Then in 2005, I full timed for 8 years without hookups, saving well over $10 a night, paying for it again in savings. From 2008 - 2013 I lived in the RV, without need to run the charger, saving energy that whole time.
Anyway you can move the solar panel from RV to RV for the next 30 years, and it will always be worth the $225 that you paid for it.
Good luck,
Fred.
