Underseal/ rust proofing products

[countrydude]

I've been future proofing my car mechanically for a while. Looking at the wheel arches I made a call to my favourite welder. I'm going to cut out the rot from my wheel arches and cut plates up from spare wings I have.

Can anyone recommend any decent products to seal the back of the plates used, also should I drill a hole in each sill and fill with cavity wax? If so recommendations on those products too please.

Also any other things I should be doing while to mood strikes me? Undersealing and the like?

[E_T_V]

Dinitrol tends to come recommended, however when I did the 200 recently I used the 3M stuff which seemed to work ok and was nice and thin (to penetrate the seams).

Once the plates are welded in, paint, seam sealer and then shutz to finish.

Inside use the cavity wax to stop it rusting from the inside out.

[countrydude]

Ok I've got cavity wax, schultz, seam sealer primer paint etc. Thanks for the tips dan.