We had the dealer install Tule roof racks (4 bicycles) on our 2000 Coleman 12ft box PUP (Westlake). I had the dealer do it because I was unsure of where to put the bases. The Westlake had the "famous" roof, but ours had 2 cross beam metal straps for reinforcement inside. I think the rack bases and cross bars actually further reinforced the roof - we never had any issues with the roof in 8 years. A couple of trips, we removed the bike racks and put a Royalex canoe up there instead.
That said, putting stuff on a PUP roof can be a real pain. I needed a small step ladder to get the bicycles on and off the roof. The bicycles/canoe had to be removed before the camper could be set up, and could only be put back after the camper was folded down. Wasn't much fun on a rainy day setup or take-down, and it added another hour to setup/takedown. If I was taking the bikes or canoe, I tried to avoid any 1 night campouts.
just my experiences