Dicor Self-Leveling Lap Sealant has been highly recommended on the Pop Up Explorer web site and is sold at Camping World
, among other places. 3M Marine adhesive caulks are also well reviewed by many users. I've had good luck with them. These products are not consumer grade and can be tricky to work with. Prepare for and follow manufactures instructions for application and cleaning up mistakes.
Eternabond tape is also highly recommended for RV roofs, but will require very careful instillation on an A Frame where it is visible all the time. I suppose careful instillation is needed for 3M Extreme too, but the neutral translucence of the backing may make it less obvious compared to the opaque white Eternabond.
D-mo, how visible is you seal? Is it obvious or does it blend in.