If you have the vehicle stripped down to a bare chassis, and the chassis is in good nick, you may as well galvanise it.
If the chassis is a bit ropey then there's not much point, the zinc won't bond properly and the heat involved may deform it.
There are a good few papers available online which will show you corrosion rates of painted, galvanised, and galvanised & painted steel. The results tend to speak for themselves!
Also worth noting that there's no way of properly protecting the inside of a chassis without dipping. If you go painted/waxoyled it will begin to rot from the inside out almost immediately.
Once you consider the better adhesion of galvanic coatings on top of all that its hard to justify NOT doing it!