[JRTJH]

If the vents are getting hot enough to produce "seared flesh" then you need to take the trailer back to the dealer and have it repaired. That's too hot, will become a safety issue either the next time the furnace is used or the day after Keystone's warranty expires. Either way, the vent is "too hot"..... I have a metal floor vent that sits about 3' from the furnace outlet to the floor ducting. That vent never gets hotter than the other vents in that line, the furthest is about 12' away from the furnace outlet.

I'd urge you to let the dealership take a look at the ducting. Seared flesh temperature is much more hazardous than "very warm" temperature. Ours is not really beyond the brink of "very warm" but is more on the "noticeably but not damagingly warm".... Yours should not "sear flesh" even in the vernacular.