Auto body repair & detailing: 89 silverado body rust, body putty, body rust

Question
I want to patch the large holes left by rust with sheetmetal, but I am doing this myself.  I do not have access to a welder but I do have drills and a grinder and I've been told I can use rivets to secure the metal in place.  Can you advise me on the best way to insure the rivets can be disguised with body putty?  I was told I could use a punch to help countersink the rivets.  Would a hollow punch be best do you think?  Also,  How far apart should I install the rivets for minimal cracking of the putty?  I'd appreciate any advice you might have.  Thank you.

Answer
The only way to do it do that the rivets are hidden is to make sure that the new panel is fastened deeper than the body panel, so that you can go over it with body filler to cover. If you grind the rivits you will jeopardize their strength and they could pull apart.