Though harder to realize in a small trailer, but a medium size solar system takes this worry out - forever. Mine collects 30-40 Ah on a really dark low overcast day. This by far exceeds what my fridge and other semi-parasitic loads like sensors drain over 24 hours.
To compensate for a typical 10-20 Ah drain of a frig and detectors in the worst weather possible, short of a non-stop torrential rain or snowfall, a solar array of total 250w will be sufficient. This is - on the worst day. On a good day it will keep running all devices that an average camper would carry, with exception of (maybe) microwave, and will harvest enough to compensate for the previous bad day. It may or may not work as a reliable source of energy for all your daily needs - depends on the location and your needs - but will definitely eliminate the need to run a genny for LP fridge.