[elhigh]

I think 30 is completely achievable. I don't think the 2.2 that was the base engine on the 2nd-gen S-10 would be any fun considering the weight you're talking about adding, you might do better with the 2.8 LK5 engine. Still a four, but way torquier. And the S-10 could be had with a pretty twisty V6, so there's heavier-duty drivetrain gear to have on this thing, no problem.

Then again, you live in Florida, where hills aren't a big issue. You could be well served with the 2.2 if you don't plan on visiting the Smokies or Rockies.

Considering you'd be sleeping close to the fuel tank and the exhaust outlet, your mention of the smell of diesel is a serious concern. It can be hard to seal up an RV. Gotta breathe, right?

I think you could crack 30 with a gas engine.