Underseal paint protection

[GTE TURBZ]

Jacked up the car for the 1st time since I bought it 2 months ago and the beam and suspension arm even the springs and i guess most of the underneath of the car is rotten. Looks like its flaking its prob due to its age where and how its been kept all its life. Ive told the body shop i want the underneath wax olyled as im getting a respray but i guess they'll just apply the stuff over the flakes.

what's the best way to restore the underneath, preventing it from corroding any further.?

Advise will be much appreciated:)

[Welsh Dan]

Remove everything thats loose with a wire brush, treat any surface rust with kurust, get any big holes cut out and welded up. Cover with red oxide followed by waxoyle and/or stone guard.