Thanks everyone.
Went with the 4" tape around the opening, then the AC unit on top. While I haven't driven anywhere, seems to hold up to the rain storms we've had.
Hopefully it works out, a little bothered by how much the roof material bunches up on the outside of the AC when you tighten it down, but don't want to take it off again, so we will see.
I did a ton of researching about installing one of these RV, but didn't see much (if anything) as to what's OK and what is not. IE is the roof material bunching up OK? It doesn't seem so (it is on the front side), but not matter what I tried, it bunched up as I tightened down the AC.
