My sympathies, Mayday. Getting nasty is usually the last resort of the insecure, and in this case, the inept.
It's done now. Your man is unlikely to be of any help. So, getting back to practicalities: if you intend to just park in there, then I suppose damp patches are more of aesthetic than practical concern.
If you do intend to store in the garage, then there's a pretty good, DIY solution.
Google "Polybond Q19". It's a roll-on, two-pack epoxy waterproof paint product. Been around for years. I've had very good results with it.