This is what you want to consider when you get to make some measurements..
You will want to mount your GC2 6VDC batteries in one of these 48-inch long metal truck side mount tool boxes. This will accomodate four GC2 6VDC batteries which will give you 12VDC at around 450AHs which should provide 12VDC at 25AMPS for a good 7 hours depending which model GC2 batteries you get. Two 6VDC GC2 batteries connected in seriers will give you 12VDC at around 225AHs which will provide 12VDC at 25AMPS for around 4 hours. 25AMPs relates to around 300WATTS of power at 12.3VDC...
For Camping off the power grid the game should be beef-up the battery system to handle what you want to run for your 120VAC appliances from an Inverter or 12VDC items direct connected to the battery bank. Then you will want to be able to re-charge the battery bank in a short three hour time using a 2KW Honda type generator with the 30AMP trailer shore power cable connected directly to the generator 120VAC receptacle using an RV30a-15A "dogbone" 18-inch long type adapter (WALMART). This is what we do with our off-road popup and are very successful camping off the power grid. All of our previous methods of doing it CHEAP all failed and we ended up in the dark around 10PM at night.
Getting the generator being able to recharge your battery bank in a quick generator run time requires a smart-mode technology converter/charger on-board. You will also need to convert your interior lighting over to LEDs.
We watch full blown free HDTV using the OTA BATWING antenna picking up the local town National Broadcast Digitl TV network (free to the public), play the DVDs, run all kinds of 120VAC items from a 600W PSW Inverter (smaller down to around 300W PSW Inverter will work but you will alway want to run more 120VAC items)...
With my 255AH battery setup (Three 12VDC Interstate 85AH GP 24 batteries) we usually draw around 20AMPS of 12VDC from the battery bank from 8PM to 11PM each night and then settle down to around 1-2AMPS until 8AM the next morning when we are allowed to run our 2KW Honda Generator for about three hours to recharge the battery bank back up to their 90% charge state. Then we are good to do this all over again for the next day/night battery run. We can cycle this 50% to 90% charge routine for about ten days but then need to fully charge the battery bank to its 100% charge state which takes around 12 hours of generator run time.
Again we are very successful camping off the power grid with our setup and running just aout everything we normally run at the electric camp sites except no Air Conditioning or high wattage microwave use.... We bring along a cheap low wattage manual white faced microwave from WALMART that works great. When you need to run the propane gas furnace then all nigh then that adds alot of current being drawn by the furnace 12VDC fan which requires close watching of the battery bank and not let it get discharged below 50% charge each night before you get to re-charge them back up. I monitor my battery bank DC VOLTAGE and when it gets down to around 12.0VDC then I know I am pretty close to my 50% charge state.
Again this camping off the power grid will require some planning and some going "GREEN" mods but your size trailer trailer is perfect for doing this... We do this all the time in our 17-foot long off-road POPUP trailer and have all the comforts of home doing it...
Roy Ken