I can see where you're heading, and if you followed the bolt on/bolt off tray arrangement it could be easily adapted to a replacement cab/chassis down the track.
We ran our F100 on 100% propane. 2 tanks, either side, hung under the tray between the cab & rear wheels. I'm sure you could mount the diesel tank in a similar location and follow the advice about a low firebox at the rear - that's going to keep plenty of distance from the ignition source to the diesel tank, and the heat from the smoker itself is no worse than that in a hot engine bay, so all the other components wouldn't be too worried. And there's always plenty of ideas for heat shielding as well.
I think you can come up with a design that works. Airbag suspension would be ideal to get a nice working height, but I do like the idea of a flip-down work platform (to stand on) - this could be on one side, and a serving/eating arrangement on the other side.
If you've got the steel, the welder, and the time, I reckon go for it. Might pay to use alloy checker plate or expanded mesh on the work platforms to keep some of the weight down.