Tom,
You should squirt some paint into your rocker panel/chassis sections before you put your carpet in. Especially because you have just welded in your safety belt brackets ... and this welding process will have burnt off any paint on the inside of the chassis rail (if there ever was any paint :)).
This may prolong the rust process ...
Pete
Rust and paint
Rather than paint, you might want to look at using a product like Waxoyl, in all of the enclosed spaces. Frame members, rockers... anything you can't get to easily, and the classic places for rust to begin.
http://www.waxoyl.com/en/produkte/120-4.htm
http://www.waxoyl.com/en/produkte/120-4.htm