Freshwater Flushing an Express Cruiser Trailer Queen

Dude_Himself

I recently purchased a 280 EC that had been freshwater kept all it's life. We're coastal, so our water here is brackish at best and salty at worst, although we do trailer to the occasional freshwater lake. Anyway, I'm anal about maintaining my toys, so everytime she's out she gets thoroughly washed and rinsed, including flushing the AC condensor (which requires crawling under the boat) and the generator (which is questionable at best). My challenges:

1. I store the boat 1 mile from the ramp, but there's no fresh water there. I normally drag the boat home to clean it up, then return it to storage, but that adds 30-45 minutes to the routine. I carry 35 gallons of freshwater, so there's little reason I couldn't use that to wash/rinse the boat. I've purchased a quick-disconnect washdown port, so I can plumb that into the system and use a collapsing 50' hose.
2. The generator is a lift pump - you don't want to pressurize the fitting or it'll push water into the exhaust and hydrolock.
3. The AC is easy - I can T the line with a ball valve past the pump, then just force water through without concern.

So, if using my onboard water supply, there's a risk of contamination if I plumb them directly in. I need some sort of gravity feed for the genny anyway, so what I'm envisioning is:

1. Use earmuffs to flush the engine.
2. install a sea chest in-line with the genny through-hull, with a vent above sea level
3. Add a float valve to the sea chest, fed by the freshwater system, with an air-gap or backflow preventor
4. tie the HVAC system to the sea chest with a y-valve

This would allow me to flush the genny and AC simultaneously with the same connection.

Any thoughts?