Now in SoCal wondering where Charleton Heston might be... Raining so relentlessly, we need him 'in character' to part the proverbial Seas. Unreal precip here...
If I built tomorrow, or remo'ed one of the small TTs I've reconned, I'd likely install and safely vent one of these:
Eccotemp Demand Water Heater
My own Japanese-inspired reuse of space would be to sink a Big Box Store Shower Pan into the Trailer Floor. I can also get a used one for a song at a local Materials Recycling Center. Create a flush, drop-in 'hatch' to cover it when not in use. Put a 3 sided Shower 'Ring' around it, as seen in Europe on many Tubs, and install a weighted bottom Shower Curtain. Such a Shower Ring could hinge down to the wall, or a few Cotter Pins could allow quick Ring detachment and storage. A Shower when you want it; open, usable space when you don't. A few quick disconnects and a Ball Valve or two would allow using the same Heater and Pump for an outside Shower, or Camp cleanup, etc.. Check Valves, as used on Solar HW Systems to prevent reverse flow, would be handy in this application.
Especially with Demand Heaters, Accumulators [Pressure Tanks for us Well users] even out pressure excursions. This provides even temp output from Demand Heaters by eliminating hot and cold water spikes endemic to Demand Pump cycling. Consistent flow in = consistent flow out. You can still flip on Sink water to prank the showering Wife, however. ;-0
In most all the World I went to on Biz, ya just don't drink the water, even at 5 Star Hotels. You drink only the dedicated, filtered-spigot water. Big Box Store Filter schemes could allow one or more potable water taps, separate from other CT/TT uses.
With thoughtful Plumbing, water from sources like a Creek could be plumbed to the Demand Pump input, which can pull a decent head. One Heater user raved about 'endless', hot Showers with such an inlet scheme. Cooties and Bacteria not killed by 110 F Water temp could be dealt with by filtering or Bleach Chlorination in an external Tank or Bladder. The key would be to not cross-contaminate potable/non-potable water by not thinking through proper Plumbing. Or, a 2nd Demand Pump for $<100- would pay for itself by Propane savings [vs. maintaining heated stored water], and absence of Shore Power hookup Camping fees.
Chlorination Links