Ok, so soap tests did nothing at all. Water immersion test kinda worked and had shown that leaks are very very tiny. That is - there is no stream of bubbles or anything like that. However, once every few minutes (yes, I spent that long staring into the damn bucket) a bubble would roll off of the plastic cap (nut?) on the front of regulators (two different regulators, actually, by Trident marine). I have no idea what it does but it was not completely tightened ("assembled in Mexico"). Also, when testing the "quick assembly" pigtail (the one with plastic external nut that hand-tightens onto the tank valve, it would never completely seal. The other kind that screws into the tank valve seals fine. With that I finally got a non-leaking regulator and pigtail assembly.
The rest of connectors are done pretty well (I did a lot of work on my hydraulic steering system previously so I kinda got to learn about all the different thread types and all that fun stuff). At this point the system is being tested over 24 hours. I am pretty well aware of changes in pressure due to temperature differences, but I am accounting for that (as well as my physics knowledge allows anyway).
There is also an "internal leak" in the system - the solenoid (Xintex one) does not fully close, so even when closed, it will allow the gas to move from the tank side of the system to the stove side, though slowly. Not great, but I don't really know if any of their solenoids are better - they all look like junk.
That said, 15 minute test passed fine (the brand new Plastimo stove seems to be closing properly, thanks for that).
Will see what happens by tomorrow.
So far grades for products:
Trident - D- (I really wish there was another manufacturer of boat propane stuff, nothing they make matches anything else they make and everything looks like cheap junk. I really would like my propane regulator to be assembled in Japan, no offence to our neighbor to the south)
Xintex (spelling?) - B- (decent electronic system, crappy solenoid)
Plastimo - B (stove works but none of the gymbals match)