Wheely Bin Plastic for undertray?
 

I came to be in the posession of a number of these bins, not sure what plastic it is, but they are about 3-4mm thick and durable, designed to be outdoors full time, take vehicle strikes and punishment quite well.
I believe they are injection moulded, but believe they could be cut open and flattened out using a heat gun.
Am planning to cut one open next week to begin work on a shallow airdam and front undertray an a Subaru
Any comments?

You should find out what it's made of.

Roughneck Storage Box / Bin | Rubbermaid

Anything made of polyethylene will be able to be reshaped with heat, but some plastics cannot do this. I think it's a good idea... if you like using hair dryers!