Been considerable discussion of this subject during the recent past. Some members have expressed doubt as to longevity/durability of the asphalt post or roof coating. Granted, the stuff is stinky, sticky, & ain't real pretty but, the cost, ease of application, & its undeniable waterproofness (izzat a word??) make it a very viable product for those who use it. I applied 2 coats on underside of my TD floor in Jul '06 & then added 1" 'blue board' foam insulation.
In 12K+ miles on near every kind of road/terrain, thru weather from +100deg to near 0deg 'f', from near 0 humidity to pulling thru flooded streets/intersections (in New Mexico of all places) where water was axle deep or higher, the undercoating has 'held up' well with no failures that I can detect. Some folks also seem to fear that 'flying' gravel, rocks, or other foreign objects may damage or penetrate the coating. After my TD was 'rear-ended' last Labor Day weekend I had occasion to work extensively underneath my TD. Other than the damage from the 'wreck' I could find no damage/deterioration to the under coating & no evidence of ANY damage from external causes. In fact, the underside of my TD looked near pristine except for a little dust/dirt, again discounting the damage from the collision -
I gotta second Greg & wholeheartedly endorse the asphalt coating, whichever type you use
