Sorry about the enlarged rivet holes, here's hoping you can find a rivet size or other approach that will do the trick!
On the sealant front, the one thing I've gathered from all the threads here is that silicon is not to be used on an Airstream's aluminum skin, inside or out. There is a range of others that can be useful, but silicon is not generally one of them.
Good ones we've heard mentioned here include:
* Par Bond (here's an example): http://www.amazon.com/dp/B007HRX62S
* Trempro 635 (modern Vulkem, it says here): TremPro 635 sealant
* Captain Tolley's Creeping Crack Cure: Captain Tolley's Creeping Crack Cure
To make matters more confusing, there's apparently one exception to the no silicon rule. This link explains what kind of silicon sealant it is and when to use it: TremPro 644 RTV Silicone Gray Aluminum
Oh and full disclosure: We're not super handy over here at Casa Rocinante - we're just doing the best we can, and often resort to our dealer for support. There are others on the forum who have pretty much taken their trailers completely apart and put them back together again in better-than-new condition, so hopefully a couple of those folks will chime in.