Hot water heater bypass valve

Looked at your floor plan. All your plumbing appears to be between the two entry doors. In that space there are only a couple cabinets where it could be. Look under kitchen sink, bathroom vanity, and pantry. You'll probably find a removable panel that hides the water heater. You'll need a screwdriver to get the panel out.

I don't have the same floor plan, but my trailer has the panel (under kitchen sink) that hides the heater. I got tired of doing all the remove and replace on those screws, so, last time I had it out, I took a 4" hole saw and cut holes where I could just stick my hand through to the valves.