Recently saved a few £ by making foams for the boys Lunchboxes. Only foams I could find were £9.99 a set and needed 2 sets. That's before tyres and wheels.  Got 2 sheets of upholstery foam on eBay for £4 posted. Enough to do two sets of lunchbox wheels on one sheet. Might do the Clod as well but the tyres are a lot harder on that so it doesn't need them as bad. You can cut this with a sharp Stanley or one of those extending snap off blades. I taped the one in the pic bu