Shelby just a wee bit more info is needed!
Out of interest which 3 sides? 
1. Bonnet, boot & side.
2.  Both sides & bonnet or boot. 
Also does it have to be folded - as in book flats or is it fixed.
As you said it is a prop & not a set piece. I assume it is handled during the performance & therefore would require being reinforced. If it is just a preset piece, could it be just a profiled ?standee?  type?

The last time I worked with cardboard was at a TV station, many years ago! It was easy to work with but it was damaged easily & tended to be too flimsy as a large set pierce, if it was not carefully handled.
Luckily they don?t use it these days because of the fire risk!
However The last time I seen a school performance where they used a  cardboard car, was for the musical Grease. They got a very large cardboard box & turned it into a car, added a further 2 smaller boxes for the bonnet & boot with gaffer tape. Then stuck on the some accessories. They then  painted it to resemble a car.  Except they went over board & tried to add real working head lights, which didn?t work & fell off at every performance!

Hi,

You might want to try a place that packs large items for shipping,or does custom shipping. I know they use large pieces of cardboard and fold them to fit.

Good Luck,

Linda

i have to make a 3d set for the beauty shop from steel magnolias in my drama class and i have not seen the movie i need some pictures of the set, it is due in a week so id apreciate it if some1 could help me out