I've used Waxoyl mixed 50 50 with new engine oil in recent years, unlike plain Waxoyl it doesnt set. So far so good where I've used it and a low cost solution so cheap to re-apply. Having a load of engine oil in chassis sections with a bit of wax to prevent it running out seems good. I don't think it would be so good in areas that get a lot of road spray though.
I have a modernish car with no factory rustproofing, and no doubt some rust (not had it long), my plan for next year though is to go underneath, wire brush and emery any rust to remove what I can, then use Bilt Hamber Hydrate 80 rust converter which I've used quite a bit. Finally I'm unsure what to use for the best protection long term, I thought that Dinitrol or Bilt Hamber products would be my choice, not really sure but will read this thread again and research the products. Its a car of high enough value to be well worth buying good products and hopefully avoiding it ever needing welding.
ive started using marine grease on exposed parts ...jet wash it all down nice in the summer and let it dry out , maybe brush a bit of oil on exposed threads /nuts etc then cake it all with grease with a cheap paint brush , good for brake pipes and thier ends etc