Coolmom, you are right that we rarely have hookups -- if we did, the light bulb solution would be perfect. And you are also right about the advantages of having the tank under the seat. The drawback is a loss of storage space. (Our first trailer had an inside tank.)
And Gordon, you are right about hot water and slippage -- I have made all of the connections with hose clamps. I am a little concerned about the vinyl leaching into the tank, but to be honest, we almost never drink the tank water -- that is for dishes and showers. We usually carry a separate six gallon jug for drinking water. That's because the tap water at most campgrounds and ranger stations (where we fill after towing with empty tanks from home) is heavily chlorinated. So we bring our own reverse osmosis water for drinking.
Having said all of that, if I had your technical skills, I would have adopted your solution, for sure. My workaround is for those of us who have no idea how to work with Pex or to wire up the system. I could learn all of that, I suppose, but the problem of freezing is so rare (first time in about 800 nights of high altitude camping!) that I am not sure it is worth the effort to get up to speed. ;)
