rustproofing inner sills

now ive finally completed my bodywork and it's all solid thoughts are turning to keeping it that way, the outside has a healthy combination of por15, seam sealer and stone chip going on. the drivers inner sill has a healthy dose of por15 and stonechip too as I had it open for repairs but the passenger sill whilst solid has nothing in it. I'm thinking of going with dinitrol cavity wax

http://www.frost.co.uk/automotive-ca...wax-500ml.html

ive read too many stories of waxoil still leaking out months later and ruining the good bits of the drive isn't in the plan. has anyone experience of applying this sort of stuff? my vague plan is to drill a hole in the rear of the sill inside the rear arch, one just in front of the b post and one on the front end of the sill, fill the sills from here then fit grommets once complete and notch the undersides of my sideskirts for future access does anyone have any better ideas?

cheers
chris

slightly cheaper and a better description here.

This page has more, but I've been toying with their drive in service... I have horrible memories of applying hot waxoyl on a driveway!