Efficiency on these types of furnaces is rather low. I don't know the exact numbers but I would expect 80% efficient or less. At 80% the exhaust will still be quite hot. Compared with a 90+ efficiency home furnace, the exhaust is super hot (my +90 uses PVC for the flue - so its pretty cool).
I also have a 250,000 BTU gas heater in my pool, 85% efficient and trust me, the flue vent is really HOT!
I think you are fine as long as the temp of the air coming out of the furnace inside the camper is 15-25 degrees above the inside temp of the air in the camper.
2011 FR Rockwood Premiere A126 Hard Side
TV=2011 Jeep Wrangler Sahara 2 Dr
Reese 66065 WDH, Curt WDH Shank #17120
Prodigy P2 Brake Controller, Mopar 7-pin Harness
B&M Transmission Cooler (#70268)