Hate to necropost, but I'm having this same issue with my frame(not nearly this bad. The 2 out of the 3 bolts on the passenger side of the skid plate currently don't torque down due to rust.
I have an appointment to have my mechanic patch it up next Weds, will it be ok until then? Does my auto trans rest on the skid plate using it as a support? Like I said, all the bolts on the driversside are fine, and the 1 bolt on the passenger side torques down nice and tight.