Own a heat gun, like a 1500 watt dual-range w/.75" round nozzle? 1200 watt hair dryer can be used in a pinch, but very slow and inaccurate. Talking about clear 1/4" PETG sheets in various sizes from McMaster-Carr in the link from OP. That stuff can be rounded over a barrel, over a bent piece of sheetmetal, and even over the backside of a piece of angle iron to make great 90 degree bends or less than 90 if desired.
Great stuff to make a custom flowing body shape for a kart, limited only by your imagination and wallet. Wallet Note: Unless you know exactly what size and shape you want to make, 2 smaller pieces that will do the job will in the end be the thriftiest route over the expensive large sheets.
Cautions: Never cut it with a reciprocating saw (Sawzall), use a circular saw with a paneling blade for straight cuts, and GO very SLOW, pressing down firmly with the saw's deck. You can use a jigsaw (I know, it reciprocates!) with a SCROLL blade for curves and cutouts if you press down very firmly and never lift up while running. Use a scroll wood blade with no less than 16 TPI, I'd advise 24 TPI, but 32 TPI (if available, is actually for metal) while slow is less of a risk of making mistakes.
You said you wanted to bolt it on/off. Use a tile and ceramics drill bit for making the mounting holes. Or hold it on with removable metal trim around the outside edges. Don't forget the foam strip between sheet and steel.
