Yup, and they do the same thing with tailgates. Drill a hole in the ends, and then run the wand back and forth through a few times to coat the inside. It's no big deal and you can't see the plugs with the gate closed anyway. It drips out the drains, but it does leave a nice film behind. It's funny...but after a while the drips stop, but then when the vehicle is sitting out in the hot sun, it will start to drip again...so it really is a commitment once you start doing this...lol.
Glad the body guy is good with rustproofing. It really is important that the product (whatever it may be) get into the right places. A door, or a tailgate for that matter, is never going to rust from the middle out...they start at the edges and around openings where the seams are.
It's a big enough business here that there are shops that only do rustproofing, and nothing else. Then there are lots of places that offer it up as an extra.
In any case, good luck with it!
This is interesting! Obviously not in a rust belt, but my truck has some rust on it in areas.
A mechanic friend said it must have spent some time on the coast, which I agree with, the truck was a RV hauler in it’s early years.
I’ve use corrosion inhibitors on this truck when I’m working on it, before putting it back together and such.
I’ve been using Amsoil HD Metal Protector and now Liquid Wrench Rust Inhibitor. Thinking of spraying the underside down with some.
https://www.amsoil.com/shop/by-product/other-products/cleaners-and-protectants/heavy-duty-metal-protector/
https://www.liquidwrench.com/product/rust-inhibitor/