I also seem to remember hearing that we weren't supposed to weld to our frames. Can't remember why (maybe the heat compromised the integrity of the metal
), and maybe it's an old wives tale, but there are quite a few who have welded the rails on with no problems.
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong, it usually turns out to be impossible to get at or repair."
-Douglas Adams, Mostly Harmless