Your big issue is obviously gonna be keeping warpage down... It's gonna happen, the metal has no real support so if your Ok with a gallon of filler in the roof go for it... Go slow, tack welds only, tack, then moved 6", tack, move, tack move.... Stop & let it cool completely every time you get back to the starting area.. It'll take allot of time & you'll get some warpage, the gallon of filler is an exaggeration (hopefully LOL)..

Like Dave mentioned it'll probably be visible later..

Like Frankenduster mentioned a vinyl top hides may evils...