rust convertor/prevention on chassis and suspension.

[boyse7en]

I want to treat the underside of my car to slow the progress of rust before the winter. Most of it is OK, but there is surface rust on the subframes and suspension arms, and in a few places on the floorplan itself.

My current plan to to clean rusty areas with a wire brush.
Wash and dry the underneath
Two coats of Bilt Hamber Hydrate 80
A coat of epoxy primer (just normal stuff from a rattle-can)
a coat of schutz underseal

Anything else better i should do or use instead?

[Astacus]

Actually hydrate 80 is pretty good stuff. Your combination sounds fine to me. You will get it all over you applying it upside down and it’s a bugger to get off.

[SlimJim16v]

I would use Buzzweld WAR instead of Shutz. Maybe look at their other stuff too.

[Skyrocket21]

Far more effective to treat the rust with deox gel (Bilt Hamber), sand it first, don't use a wire brush, it polishes the metal. Can be tricky being upside down, use clingfilm etc. The deox gel uses phosphoric acid.

The epoxy needs a good keyed surface to bond to, it can peel off without it, you can use Bilt Hamber Zinc / electrolux first.

The better epoxy would be Jotun Jotamastic 80 / 87 / 90 winter grade, they also do one with aluminium or zinc. The numbers are the parts or thickness.
Epoxy likes to stick to keyed metal, creates an impermeable barrier. Without a good keyed surface it can peel off, if too thick can chip. You can overcoat with what you like avoid acid such as etch primer etc.

I don't rate Hydrate 80 very highly, probably last 6 months, it's like a polymer coating with some rust treatment.