Carrying stuff on the roof

I'm going to pull the trigger on a relatively small inflatable boat (likely, the Intex Mariner 4) to get me away from shore while fishing on camping trips. The inflatable which I'm looking at can fit into 1 or maybe 2 medium sized duffle bags. Or possibly a medium to large tote. Due to restricted amount of space inside the camper, I'd like to transport the duffle bags or tote on the camper roof. BUT...I don't want it rubbing a hole in the roof material.

Anyone else on here strap bags and/or totes to your roof and, if so, how do you prevent those items from doing damage to the roof?

Pics are appreciated!

TIA.