Last camping trip I fired up the furnace in my 3170ds. I found that no air (hot or cold) was coming out of the rear vent that exits under the bed in the back. While winterizing today I removed the black plastic cover in the water pump compartment to fix something and found this.
Apparently FR didn't think that the 4 inch bolts hanging down would puncture the foil duct pressed up against them when the cover is installed. I repaired the duct (in 3 different places) but still have no air exiting the vent. I think the duct is pinched closed where it attaches to the furnace. Everything is so crammed together in there I think this particular run of duct is collapsed.