While an experienced framebuilder would no doubt be better, I wouldn't worry about this too much. If your guy is an experienced welder, just make sure you've got it all measured and laid out correctly - it'll turn out great.

I've built a couple bikes with a buddy and his friend who can weld; they've both turned out great so long as everything was communicated clearly and there was no confusion.

Post some pics of the Marauder as it comes closer to completion... I'd really like to see how it turns out.

Mike