I've been following this thread closely, because I sold my Kimberly Kamper, that had a Webasto (same as these Chinese knock-offs) heater. The Webasto helped me extend my camping season and I missed it this fall. I thought I'd throw out a few of my observations from using my Webasto nearly every spring and fall for 10 years, to assist you with your prototypes, so I can copy (haha).
First and foremost, the amp draw and your battery ah capacity/health are critical. I had 210 ah batteries in my KK and could start the heater on the first night and run it all night (on low). The second night I usually had to charge the batteries with a generator, or run the truck with the camper attached when I started the heater, until it got going. Low voltage meant it would repeatedly try to start itself, worsening the low battery issue, until it finally threw an error and shut off. The other thing that has been pointed out in this thread, is that the fuel supply doesn't tolerate air in the line well, which was an issue with my KK, because I was running a hose from a small fuel can, or from my tank when I had a diesel truck. That would cause it to restart and eventually cause an error code and shut down too. Priming it properly and maintaining flow without bubbles in the line was critical. It was also real picky about any restrictions in the intake/exhaust hoses. One of my guest kampers inadvertently blocked the intake/exhaust ports with his high dollar down bag and pad. His bag and pad got soaked in diesel and caught on fire, nearly burning us all down. Needless to say he was not amused and neither was I (got to test my fancy halon fire extinguisher though).
It was enough of a pain at times that I hardly used it unless it was super cold (like 0-20f) . I was glad I had a wood stove too, but when things got really cold during elk hunts, I was very happy to have the Webasto running all night. On high the thing would cook you out of my KK, which was all canvas. I could even keep the large enclosed awning area warm with the thing, which made my guest kampers happy. I generally ran it on low, so that the fan noise didn't keep me awake all night. On low it was quiet enough and created white noise to help you sleep. It was only rarely run at elevations below 8000ft, and that may have contributed to the above issues, but once it got going it ran cleanly and the exhaust and smell was very minimal. I had about 10 ft of exhaust tubing and ran it up and away from the sleeping area. I never knew it could "coke" up from not running it on high and that may explain why it was a little fussy the first time I ran it each season. There were only a couple of times I couldn't get it going and I believe those were related to the battery and fuel supply issues mentioned above.
FWIW, my Webasto manual wasn't much help either. It had a lot of tech specs and for most error codes it told you to call your dealer for most things. This thread has been enlightening and I hope you keep sharing pics and experience with your designs, as I'm now tenting it again and missed out on elk season this year, because it was only supposed to get into the 20's, during the week I could go, so I chickened out. Growing up in CO, winter camping is something only the transplants and newbies get excited about after experiencing it without a heat source a few times. BTW, Mr Buddy Heater isn't your friend above 7500 ft, it won't stay lit for more than 20 minutes and just pisses you off when it's really cold.