replacing door cards but keeping original vinyl

I am replacing the door card on the my bay with some 3mm MDF and recovering it with the original vinyl trim. I am having trouble getting the vinyl to stretch over the new card and it seems to have shrunk slightly. Anyone got any tips. Would a low amount of heat such as leaving it in the sun or under an IXL tastic bathroom heater help.
Thanks Nicko

Hair dryer, I used a standered hairdryer to stretch my padded vinyl cover for my Square and the stapled it to the back. It was from an early dash and mine is a late Type 3 so it was different in shape, hairdryer sorted it out in no time, they could have been made for each other.