Was lookin back thru old posts and noticed your questions.
We own one of the Hartline showers and love it. Short of this sounding like an ad, we have plenty of room to stand and shower in it in our sleeper. I put a small d ring in one of our screws in the top of our sleeper and it holds the top fine.
Our concern was going to be how hot the water would get. We bought the shower at the Louisville Truck Show, filled it and plugged it in before seeing Charlie Daniels. Let it continue to heat thru the night, and the next morning the water was actually too hot for my wife! Timing is everything for temp control.
The big positive is that if you've delivered somewhere on Friday that doesn't have a truckstop close by, and you just want to hang out there for the weekend, you've got your own shower.
My wife and I can both do a "Navy" shower with about 2.5-3 gals, so the 6 gals is fine. The downside, the nozzle is directly over your head. My wife finds that she would like some sort of hand held nozzle.
All in all, a great product.