I have a Planar diesel heater
. It's a similar, Russian-made version.
You hit on two very important areas to consider. To answer your first question, yes, that's the right thru-hull. I bought the straight version, but if you can make it work
with the angled one, that's even better to keep water
These units were built for trucks and RVs. They want to vent directly down below a metal chassis. The exhaust
hose gets VERY hot, like 700-800F (375-400C). And if the exhaust hose is too long, the combustion chamber will overheat. How long is too long? Who knows. But remember it's designed to assume a very short run, maybe a foot or two. Likewise, the combustion air intake should be outside air, but again, any restriction from a hose can restrict the flow and cause overheating
You will have similar issues with ducting. The fan for the cabin
air is not designed to move it very far. And if the flow is too restricted, again, you'll overheat the unit.
One option might be to use a booster fan in the duct. I did that on my last boat
for a long air conditioning
duct and it worked pretty well. Since the air conditioner only ran on 120VAC, I used an off-the-shelf duct fan from a home supply store. A 12V version would probably require some searching.