Skidplate...Yes.

Bear in mind, I'm coming at this from the kind of trails and wheeling I do.

Mine are made using 1/4" wall 2x2 square tubing, w/ 2 attachment points welded to the frame. (I've got a long wheelbase LWB)

During impact there is some deflection (less than 1/8" and the clearance to the seam is about that. If it were attached, my seam would be bent along the whole length an 1/8". Some say that you'll have added strengh because being attached to the seam add's to the overall strength but I believe in the weak link theory. i.e. the weak link will fail first.
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