One of the most valuable - and sometimes frustrating - things on this forum is the SEARCH functon. Please check this thread of only a few days ago, and in particular read LEWSTER's first posting.
The inexpensive Chinese portables are NOT safe in a trailer. There is a reason they are always shown hanging from a fence post or a tree.
One person CAN take a perfectly acceptable shower with six gallons of hot water and the conventional heaters only take about 10 minutes to reheat the next six gallons. If the campground has nice showers - take your 20 minute scald there!