Frame Stiffing to reduce Porpoising?

mkirsch wrote:
To paraphrase, "If you find somebody willing to weld on your frame... you don't want them."

Why not? Thousands of commercial truck frames are welded on a daily basis. They cut 'em behind the cab and splice in a piece to add length. They install frame liners to add strength.

Older pickup trucks are routinely shortened to convert them into the more desirable "short box" versions.

Stock frames are boxed in all the time for offroad applications.

Thanks for the comment. This was along the lines of what I was thinking when I asked the question. I know it isn't common and you don't want just any shop doing it but clearly there are places that do it for the reasons you mentioned.