Definitely don't do it all in one go! I'm not the world's best welder either, but I have welded some non-structural stuff in alternating / start and stop / weld and wait passes, and still managed to warp the metal - and it was .25" also. It's gonna take a while, but I would run a couple inches and then switch to the next rim and so on. Especially with something like adding beadlocks to a rim, I know I wouldn't want to rush and end up with a useless rim that is warped - even with a trail-only rig....