I have the water heater out of the Gulfstream now.... Part of what I was talking about in the original post... It has a manifold next to it that has both cold water flowing in and hot water flowing out... the manifold failed, internally and externally when the water heater went, and apparently is irreplaceable; I’m going to have to bypass the manifold, run independent direct lines, with regular Tees instead of complex manifolds; input to the water heater and then out to the faucets etc.
Ours is replaceable for about $300 on Amazon but Mr. GG2 looked at it and said if it dies he’s going to let the RV tech fix it.