Easy job - Lay the new vinyl on top of the old. Only a couple of mm thick so no issue with door clearance etc. unless it is very tight. For the dent fill it with rubber solution or liquid adhesive (evo stick or similar) until it self levels and sets hard. Make sure the new joins are well away from the old ones.

Only thing is, if you go that route, it becomes twice as hard to take it up should you ever want to. Ask, in your best Catherine Tate voice, 'Am I bovvered?'

Good luck.

DtG