They won't be used outside, but may get exposed to rain/weather whilst

being

transported to/from events (wedding receptions/hired halls/dinner&dance).

So was thinking of waterproofing and either covering with carpet or
hammerite to preserve them whilst they return to me a tidy income.

Make sure you have some kind of dolly to move them and some help. You
don't want to drop the cabinets because they will crumble where they hit
the floor. As for waterproofing, a good marine paint should work just
as well as all these other options and be much cheaper. Make sure to
make a cover for the drivers that is weather resistant for moving.