I enjoy a bit of carpentry. I often recycle pallets or buy sheet plywood/MDF/melamine.  My current transport method is to use my boat as a trailer.  This works, but it's really too big to be practical for M10 etc carparks.

Then I had a (potentially) cunning idea.  Our SUV has a hitch receiver.  I could make a rack to hold pallets and plywood.  I'm thinking something like a toast rack on a giant scale with two or three slots, three tie down points per panel, a duplicate plate hodler and trailer lights.  Not that different to a heavy duty bike rack.  A couple of hundred dollars worth of steel to make, plus a slab for the welder. 

The vehicle is >1.2m wide and close to 2m tall.  The panel rack would only be used in the 50kmh zone. There would be little windage acting on solid sheets of plywood and almost nothing on pallets.  

The hitch is rated for 250k down-weight.  As a rough guide a sheet of 25mm plywood weighs 40kg.   I can't see a downside (assuming appropriate build quality).  But I'd appreciate other people's thought on risks.