Just a guess based on your intended use (2 days/3 nights max per week, couple hours of TV a night, minimal lighting or LED lights) with trailer parked in relatively good sun. I would start with twin 6volt GC2 batteries, 100 to 125 Watt solar panel, a 15 or 30 amp PWM controller and 300 MSW inverter plus necessary wire and materials. See how that goes and could add another 100Watt solar later if not quite enough
less than $500 all in cost with self install.
A 30watt system is not much more than a battery maintainer (in fact 30 watt solar is what I use as a battery maintainer on my boat)