Lewis,
Good luck with everything and please understand I'm not suggesting you don't pursue the avenues you are, but having worked at the both dealerships and independent rustproofing companies want you to know and keep this in mind as you go.. Rustproofing, interior and paint protection products purchased at the dealership level also most independents have become more so just additional options or services to sell than concerns for the materials used, any application process or long term product success..
Whether done in house at a dealership or contracted out to an independent, what products are used or the thoroughness of any application process means nothing to a dealer who's only concern is the bottom line net cost verses the amount he can sell it for...especially when the warranty is carried by someone else!.
If you want product sucess more than a piece of paper warranty, paint and interior protection products can purchased and applied with more care and concern on your own...and should always done before the rustproofing process!.
For real rustproofing, it's best to find someone who has the equipment and applies aviation developed products like Boeshield or ACF50's automotive variant 'RustCheck'..
~ Pete