I am not sure what gauge mild steel it is, but I can't imagine it is any thicker than 14. As far as armoring it or sleeving it? Yup, try a search. I used 3/16" angle, varying between 2 and 3 inch legs where space permitted. It's tricky working around all the lines running down the driver's side interior wall of the "frame", so I armored the outside and underside, also giving me good places to mount skids and rocker armor to. And what type of welding shouldn't matter, so long as it is solid and quality. I know folks who used a 110v MIG in their garage, and I know a guy who used 1/16" Dualshield wire at the shop I work at, and I know stick should work just fine. So find whatever material will work for you, as nearly anything solidly fastened will be a good leap in rigidity.
-Rich
