I can't tell you how much ACF50 and Bilt Hamber's cavity waxes have been sprayed inside the cavities, sills, doors, inner wings, inside the chassis (loads gone into and over the rear crossmembers), nor the amount of marine grease that's been spread over the chassis and the outside of the inner sills, followed by the twice yearly blow over with ACF50 over the whole underside.
It's the only way i've found to keep on top of the rust, you need stuff that will creep, yes it washes off and no adequate rustproofing is a one off job in my experience.
I've sprayed loads of stuff into the areas MIster Cruiser mentions, haven't pulled the tank out but can't see anything to worry about, yet.
Yes its a messy bugger to work on underneath but i'd rather that than have piles of rust dropping in my eyes every time i looked too hard at the underbelly.
So far, and it's 19 years old this year there's never been a mention of rust bar the odd advisory about front brake pipes...though multiple mentions about the whole underside being coated in 'underseal', which it isn't.
I like this vehicle a lot, yes it likes a drink but it does everything we want.
Mrs visited family think it was Boxing Day or the day after, coming back up the M1 the heavens opened and sheets of rain came down flooding the carriagewway, she's doing 70 at the time same as many other and the 120 just ploughed through the stuff without a murmer allowing her to gradually redice speed to sensible visibility, it just does all you ask with no drama, you can't say that about all vehicles.
My 70 series saved her from any hurt some 20 years ago, no airbags no crumple zones but the accident she was in a tough battering ram was the best bet, had she been in her little company Punto at the time things might (would) have been somewhat different, these Toyotas literally take some beating.