I must admit to appreciating this thread quite a bit 'and' learning a lot - especially with respect to water heating and his approach to a conversion using external access. Ingenious!
Regarding helping a neighbor with a van conversion, and the job being poorly built, I long ago learned there are differing standards of acceptability. That, and virtually all were below 'my' standards. Thus, I try really hard to bite my tongue and just help when asked because some of these people are not blind to the differences and are doing the best they can.
For example, a fellow I once helped with a model airplane was doing a **** job. I mean everything from poor glue joints where glue made the joint instead of balsa, to wrinkled covering, and crappy equipment installation, everything was at a very poor level. Turns out he was raised by his mother alone, e.g. no father, brothers, uncles, kindly neighbor, or any men. Absent a Dad to show him how to do anything, he was literally doing the best he could.
So I took to doing something part way whilst explaining what I was doing, then asking if he'd like to take over. And then watching carefully and offering pointers as he completed the task. Same technique I use with my grandson. He's getting better and could fairly be said to now be working to a good standard without my help.
The point being, despite my level being what I think of as quite good, I'm sure there are amongst us those who would look at my work and say it's ****, also! Takes all sorts and it's a credit to our friend he is helping the fellow with the **** RV conversion. If I were a betting man, I'd suspect that fellow will come out of his experience doing better and if he ever does another RV-conversion, it will be better for his experience with this one.