>
>I've been checking around locally and the only rust prevention stuff
>available and suitable for injection into frame heads etc is by a company
>called Crown.

This may be a split-off company from the Rust-Check people I favour, 
happened years ago, and Crown has always been slightly cheaper than RC$130+. 
The stuff sounds the same, it has a slightly pink tint, sweetish oily smell. 
Go to Candian Tire and buy a large tin of RustCheck spray, $7.99 and blast 
away. You'll need 4 tins just to do the underbody alone.
        The older busses have LOTS of sealed cavities, ie. the rockers, 
fender lips, door uprights, front wall/beam behind bumper etc. There is a 
lot of drilling to do, unlike in a Vanagon. The $100 is a very good deal if 
you make sure they do a really complete job. After that, DIY with the spray 
tin for annual touch ups.
         Buying 5 gallons is way overkill, even 1 gal and garden sprayer$$ + 
your labour is over $100. If your van has small plastic plugs on each side 
of the engine compartment at bumper height then pull'em out and tell the guy 
to run a 6 or 8 foot wand up there so he gets the inside of the box members, 
my '78 was so equipped, there is no other access except with lots of 
drilling.   tim s.