I have a Roadtrek van, so all self contained for living, but have been looking at enclosed trailers to carry extra water, fuel, and food (and cat litter).

The one thing I keep running into is weight of the trailer and what it can carry versus weight of the fuel and water (and litter).

I keep crunching the numbers, and for what I would lose in mpg it doesn't make sense to go too big.

Naturally, the Roadtrek only gets about 11-12 mpg fully loaded ( full water tanks, geared up). With a more efficient truck and a big trailer the numbers may get better.