Hole Repair

[Seventy468]

I have a 12' aluminum fishing boat that has 5 holes (roughly anywhere from 1/2"-1") I took it to a professional welding shop today and they said they couldnt do it because it would make the original pop-rivits leak. When I purchased this boat it had water weld in all the holes (that I overlooked) and luckily noticed it before I put it in the water. I really do not want to put water weld back on it for the fix... so I was thinking pop-riviting a piece of metal (what should I use, steel or aluminum?) over all the holes, and use a silicone that is great with water. Any other ideas? I am new to this site and new to boats, heck I just wanted to go fishin! now I got a boat to repair

Thanks for you help and time!
Seventy468

I have a photo of the area that needs work, however its to big or something wont work for this site, if your interested in seeing/helping you can go here (my webshots page) http://good-times.webshots.com/photo/2532997020103976893oFdsOL