If the vinyl's already cracked you can try and hit it with rapid remover. I've found it works great on baked on adhesives and the cracks should allow it to soften the adhesive somewhat.
If I have adhesive left behind after removal, a few quick squirts of the stuff and 5 minutes later I can just squeegee the adhesive off as a big goopy mess. With cracked vinyl you may find it all comes off together with a few applications.