Oh God. Not again. If the weld cracks, it's cos the weld is ****e. I'd TIG seam the mounts and any panels running crossways. The rest can probably be MIG stitched (although the MOT man would like it to be MIG or TIG spotted, first) which will give some (more) give in the event of an accident. This is (or should be) irrelevant if a cage is fitted (properly).