I am going to attempt to make a Scooby Doo Mystery Machine Van for my cousin's 9th bday. I would like to place a 3" styrofoam square under the van to raise it off of the base board. I will adhere the stryofoam to the base board using double sided tape. Should I just use the same to adhere the board that the actual cake is on to the styrofoam square or is there a better method? TIA.

When I attach styrofoam to a board a push a nail from the bottom of the board into the dummy. hope this helps.

For my Mater truck I used a dowel and ri

No just through the cake and styrofoam, styrofoam attched to cake drum using double side tape, probably could use ri too.