We had a '93 Jayco 1208 PUP that we bought new. One of things they touted in their sales literature was that every Jayco PUP roof could support cargo racks for bikes, canoes, etc. Of course they had their own and we bought them because I didn't want to chance mounting them myself at the time and damaging the roof. We also bought the Jayco bike rack which was a mistake because it scratched up our bikes. But the cargo bars were great.
The brackets were mounted to the edges, not the roof itself. The rack bars in this link are very similar to the ones installed on our old PUP.
I'm not home right now, but If I find a photo of our pup with the bikes on I'll post it.