Welding anything to the flange of a frame rail is a really bad idea. If you want to secure a bed block to the frame, either bolt it without welding, or add a tab that can be welded to the side, not the top of the frame. Weld beads cause stress risers on frame flanges and you'll end up with a crack across the flange beside the weld.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!