There are four large holes capped with plastic plugs on the chassis side members, once the plugs have been removed they make ideal entry points for the Waxoyl tube/nozzle.
The boot floor chassis legs are open at their ends, so very easy to spray.
The rear crossmember has no access holes, so they have to be drilled. The easiest place is at its top face. Moisture does not find its way easily through this box section, so it does not rust often, but it's a pity to omit when waxoyling the whole chassis.
The front chassis longitudinal members must be treated. Again, there is no external access; the easiest way to do so is by drilling the toeboard between the spot welds that hold each longitudinal member, and guiding the spray tube into both upper and lower rails.
Depending of the chassis there may or may not be a large hole at the middle of the toeboard, below the heater. This box section must be treated, too, and an access hole drilled if not present.
The middle crossmember has very easy access, the same goes for the front one (through the starting handle hole).
It would be beneficial to remove the foam that has been known to destroy rear suspension mounts by absorbing moisture, but it seems impossible to do so without cutting open the ends of the chassis side members.