We installed the dorm fridge in our 25 year old Sunline 15.5, and used it for three years. Most nights we were powered but in Labrador that was not the case plus we had some days we drove for more hours because we were averaging 25 mph.
I began by testing it in the yard for a few days to see how it would work. I began by running it on AC to determine what its normal duty cycle was once cold, i.e. minutes on versus minutes off, the higher the ratio the better.
Also we keep our fridge pretty full, it increases the cooling down time of the fridge when not powered. Think of a full fridge like having a block of ice in there.
Having the ability to charge from Solar
panels and the tow vehicle should go a long way towards meeting your needs.
Here's a little perspective...
It may be true that the fridge draws 100 watts from the battery but as I recall it does it for less than 10 minutes out of every hour or about 15 watts an hour. Compare that to a traditional trailer light
bulb. A traditional light
bulb draws 2 amps or 24 watts an hour.
If your inverter draws 1 amp on standby an hour that's equivalent to 12 watts an hour or half of a standard trailer light
You did not mention the price of the Inverter. If it's very much, remember mine was only $59, you might consider getting the real thing, a 3 way fridge.
We installed a dorm style fridge because we planned to own that trailer just for the trip to Labrador, 2 months. Fortunately we liked it and that 2 month tri[p really extended into 10 months and now 5 years of towing small trailers. If I had been thinking long term I would have gone for the 3 way or at least 2 way fridge.
I liked our dorm Fridge better than our present Scamp
fridge because it was bigger than the small one in the Scamp
however I appreciate the 3 way when out of the way from the grid.
Hope this helps.