I agree with J Francho - fix the rivets. It is not hard.
First of all - I have been through this - this is what I have learned:
1. JB Weld does not flex...so as it will temporarily solve your problem...the first time you hit a big wave or your aluminum flexes, the JB weld will no longer work. I recommend 3M 5200. This stuff seals and flexes...trust me.
2. It is easier in the end to replace the rivets. The hard part is finding the right size rivet to go back in there. There are 2 measurements when looking for the correct rivet. Shaft length and shaft width.
A. I also have truss head SS phillips head screws with lock nuts as a backup plan for the rivets if I drilled the hole too big getting the old one out.
B. Easiest thing I have found to do when getting old rivets out, is to get a chisel and chisel off the flat side (from the inside, if it is accessible). Once you chisel that end off...punch what is left of the old rivet through the hole by hitting the shaft. If the rivet is not accessible from the inside - then you have to try the same technique from the outside - which may lead to you having to drill out the rivet...making a hole bigger than you originally planned...which the Truss head SS screw and lock nut is once again a good solution.
3. When inserting new rivet/screw...be sure to coat hardware in 3M 5200 sealant - let it cure for 24 - 48 hrs and you are done...good to go.
I have never used the flex seal. From what I researched, it added weight...and it was not a sure fix. I want(ed) a permanent and for sure fix.