The chassis wax is available as an aerosol but also, more economically, to use with spray equipment. We're using the same gun here as we used for the Fertan rust converter.
The tube is pushed fully into the chassis member and the gun is activated only as the tube is being retracted. Only a small amount of wax is needed.
Doors are treated in just the same way.
Closing the access to the doors.
The drain holes
Fertan rust converter to kill the rust, flush through with water, allow to dry, spray with wax. The wax has a useful working life in excess of 15 years use on a normal, well used vehicle. We know this because we've been making it for 15 years and it is still going strong on the original test vehicles.
It would be nice if all vehicles were this good prior to preservation work, but a few holes and a little washing do go a long way to getting to a similar state.