Rust proofing Products and application

[T1pper]

I need to get some waxoil or similar product on the underside, behind the wheel arch covers and in all the nooks and crannies of the Land Cruiser before the salt hits the road.

Two questions what is the best product to use and does it has to be bone dry before application?

I was intending to jet wash the crud of underneath and behind the wheel liners and wondered if it had to be totally dry before application, will the water be expelled or held under coating?