Taking the plunge and starting to mud the ribs for riveting. Laying up for 24-48 hours, and then going to rivet on Sunday/Monday. Did just two ribs tonight. Trying to get the process down without creating too much mess. Think I'll go to the Dollar Store and buy some disposable mixing dishes for the pro-seal.
In the end I used a tongue depressor to mud the rib flange, kind of like I was going to lay bricks. Made sure everything was covered and then slapped it in place. The ProSeal acted like a lubricant and it was actually easier than I thought to position things once in place. I still need to figure out how to keep the rivet holes clear. I tried my best to wipe away excess using Acetone and sometimes MEK, but I'm sure the hole is still fouled.
Cleco'd in every hole, and also beefed up the cleco tension by installing a #6 finish washer along with the cleco. We'll see if it helps. Could not really discenrn a difference.