[SVAuspicious]

The D4 is probably marginal for a 42 footer. That said, it is better for a diesel heater to be too small rather than too large. They don't respond well to running at low output. The PNW also doesn't stay all that cold for all that long either. If it is really $400US I would grab it and accept the limitations.

When you get a fuel pickup it makes sense to cut it short so that the bottom of the pickup is an inch or so above the main engine pickup so you can always get the engine running and to a fuel dock. *grin*

 

[SVAuspicious]

Pull the case off and see what the combustion chamber looks like. If you can swing a Facetime or Skype video connection I can "look over your shoulder." It may appear intimidating but taking those things apart isn't hard. Rebuilding one is fussy. Parts are expensive(ish).