Edge welding 1/4" sheet to minimize warping

[RAyJ]

We are working on a built in storm shelter/walk in vault. Due to weight restrictions we are planning on using 1/4" sheet (4x8) steel edge welded instead of the usual reinforced cinder block and concrete walls. I'd like to mig weld from one side only but will likely smaw it outdoors. I'm looking for suggestions on which rod and current settings to use to minimize warping without having to flip the plate over more than once (twice at absolute most). room size will be 8x12ft minus trim. The finished panels will be dressed out with interior studs for plywood or sheet rock.

have a MM211, TB302, and a CP300 at my disposal.

Thanks

[FusionKing]

Mig is generally less heat, (IMO) even then you have to be careful tho.
Welding the perimeter will cause a good amount of grief if not done with care.
Using 1/4' should be much better than just sheet metal tho.
I prefer 7018 for stick

[WillieB]

I don't sew, but I think it is a good analogy, sew two pieces of cloth together, iron it, it lays flat. If in that seam you sew a strip of stretched elastic, it ain't going to lay flat! Filler metal fills a space with little or no stress, As it cools, it, together with the heated portion of the work piece will shrink. Across a weld bead, shrinkage is not significant, lengthwise it is pretty severe. Could you settle for a series of 2" long welds with a few inches between. If a continuous corner is important consider a strip of angle steel overlapping the joint a lot less weld bead would be needed. Might you build a frame, then plate over it welding only intermittently.