Chassis Stiffening foam/welding

[brianhaygood at gmail.com (Brian Haygood)]

Hey all.  I know people stiffen unibodies by welding the seams.  What scares
me about this is the idea of setting fires inside my roccer panels (yes, I
spelled it that way on purpose) and removing all rustproofing and paint in
the process, not to mention wiring. Here are a few questions...

What are the most important areas that seam welding can help?
How do you prep for it?
How do you clean up and seal the metal inside and out after you do it?

Any insight would be appreciated.