Most of what you want are rather easy modifications, just buy a door side kitchen model and rip into it. Hide the toilet with a curtain or divider, replace the countertop and install the small sink, now just eliminate some storage by eliminating the areas that intrude too much. All of this is basic carpentry skills and basic materials. I've done much more than that to customize and improve mine.
You should be looking at important things like tire and wheel sizes, carrying capacity and structure. The thing is of little use if it is barely roadworthy. Try to eliminate the marginal trailers and only then pick and choose from the few that are left.