actually any home, its easier to work without water draining
back on
you,

and nearly impossible to solder copper lines with water in
them.

CY: Right, it's impossible to solder wet lines.

2 valves elminate all this.

CY: That's true. But you have to solder on the valves.

and what difference does a frame home make?

mine is brick but the water system is the same.

CY: The trailer I live in, the top of the WH is about three
feet higher than any sink or tub or toilet in the place.
Won't be that hard to drain the water out of where I'm
soldering.

the only time both valves are closed is during tank
replacement.....

CY: True.