What was in there to start with were pop rivets, but they went through the top of the belly band, and through the two fiberglass lips (one from the top of the trailer, and one from the bottom), but not through the bottom of the aluminum band.... How they ever stayed on is beyond me. A lot of the holes were broken out...and I tried to fix them, but figured I'd just drill new ones and then put in SOME kind of fastener. I saw this one and thought that might work great...the trick is finding them locally.
RIVETS Non-Removable R-Tite Rivets ITW Fastex
I'm concerned that regular pop rivets would have nasty edges hanging below the belly band which would catch on stuff... These at least would be fairly flush.
And I would never use caulk of any kind...especially after having to fight getting the old stuff off the trailer to start with. I was thinking I might put a strip of butyl tape under the aluminum band before I attach it with rivets to keep moisture and debris from working down underneath it. Is that a good idea or not?
Of course, the small bolt/nut thing might be the answer. Cheap, readily available and can be removed without too much damage should we ever have to replace/repair the trailer/belly band area.