Very cool and great idea, Steved0x!
I used the following online company to create my magnetic decals (seal grey Boxster thread).
Was one single sheet, before i cut it. Fast, easy, high quality and low costs:
100mph...no problem...they probably even stick @ 200mph
http://www.vistaprint.com/category/magnets.aspx?xnav=swsProductOnly_ResultTitle
I am sure, there are more companies out there with equivalent offers.
