I installed the gas webasto gas a year ago. I have not used it a lot, sometimes at altitude and only when it is below 50 outside (actually mostly when in the 20's F) so far, no problem, but I probably only have 50-100 hours of use total. It came from
Heatedupamerica via Amazon (they seem defunct) The supplied unit was clearly made in Russia and when I called the vendor for support (the supplied harness didn't support the Rheostat) they immediately shipped me a replacement that was "universal" in that both the digital and rheostat work.
Connecting it to the aux port of the fuel tank was pretty easy aside from multiple trips to NAPA to get the right size hoses. I purchased a rheostat to apply the altitude adjustment detailed in FarOutRide. I never did the adjustment and I only use the Rheostat and, so far, I only use the lowest setting even when ~20f outside. When super cold the burner comes on maybe 30-50% of the time and the cabin stays mid to high 60's which is fine for snuggling in bed. Per the spec a night of heat (12h) should only burn .9g (less than .5g at 50% duty cycle) and indeed, heating for a couple of nights made no appreciable difference in the fuel level.
I can't imagine why you would smell either gas or Diesel as all that should be external to the cabin. If exhaust is being sucked into the cabin then something SERIOUS is wrong. Fix it.
The only reason I picked gas was to avoid a second fuel source. My goal was an all-electric van. I certainly wasn't going to have Diesel anywhere inside the cabin and I was nervous about having fuel under the hood (a safety hazard in a collision) and I didn't consider putting the tank under the van and use the DEF port for a filler (a friend is doing that, what a pain).
OTOH Having the alternate fuel source can't drain your main fuel tank. If I were to build a second van, or replace my current heater, I might reconsider a cheap clone and 20l aux fuel tank somewhere under the van.
I mounted my heater behind the drivers seat over the void just behind the filler tube for the main tank. That way I used the filler guard to shield the fuel and electrical lines going to the pump. It is buried in my raised floor behind the swivel seats.