There's more than one way to skin a cat, although the right way is what Ted say's- weld in new steel. BUT, you could also remove the t/lamp, clean the edges of the hole down to steel and use any one of a variety of fillers to bung it up. JB Weld is good stuff or short strand fibreglass (Tiger Hair) could be used, but you'd have to put in a backer to prevent fall-through and then be skilled enough to carve the majority of the filler out and re-configure the shape of the original panel; remembering that the inside has to be friendly to the t/lamp gasket to seal properly. If you're good with filling/sculpturing, go for it- otherwise get out the torches.
