If you decide to rust-proof your Miata, give Z-Bart a look (might be Zbarth). We used them on my wife's last car in Chicago and it seemed to do well. Annual inspections and not cheap (maybe $500 for her 1994 Oldsmobile SUV), but they've been in business since the 1970's and her car was clean when we brought it here to TX. They also offer warranties on clean used-cars (as in, you don't have to have it undercoated from the showroom floor). Stay warm, my friend.