I have never tried that particular stripping job, but I would try Castrol Super Clean (lye-based cleaner which works as paint stripper). Next is Testors (ex. Floquil) Easy Lift Off, and Scalecoat Wash Away paint remover. I have used these on various brand paints with various rate of success. Keeping the stripping solution warm improves its stripping action. By warm I mean around 80-100 deg. F. Since it is now summer in NJ, just doing the stripping outdoors on a warm day should result in ideal stripper temperature. As usual, although all those strippers are supposedly plastic-safe, I don't take responsibility for any shell damage. Castrol is the safest for plastic.
EDIT: forgot to proofread.