If you boondock or go to campgrounds without hookups the limitation will be the fresh water and black water storage tanks. A 20# propane tank lasts us a month with it being used for cooking and heating and the fridge. More important is the capacity of the battery bank. I would want 400 AH of battery capacity.
If you figure the maximum payload weight and multiply that by 4 you will have the maximum wet weight of the trailer to tow. Subtract 1000 lbs. to have the approximate dry weight of the trailer.
Appreciate that the longer the trailer the fewer public campground spaces you will be able to fit into unless you relegate yourself to the RV trailer parks where overall length is usually not a problem. Big decrease in California if your trailer is longer than 28 feet and the shorter the better.
If you get a gas powered truck then do get the 4.10 gears. They provide 25% greater towing capacity over 3.73 and 50% greater than 3.42 gears. Easiest way to improve overall performance when towing and also be able to accelerate better when merging into traffic.