Maybe I’m just a gorilla, (who lives in the land of potholes and darkness) but I’ve never had luck with something held together With cotter pins, or made of aluminum. I also am too big to drive a subcompact, so the “folding” thing is secondary. I still have one or two hanging around, but about 10 or 12 years ago I found a small two wheeler that is one welded piece of steel with 5 inch “solid” PE wheels. Can easily be squeezed into any load. I bought it at Sears for under 15$. If I expect rough terrain I secure the cab etc. with bungees or rope. I have mostly lighter gear at this point, my main cab being a 2x15” that weighs 60 lbs.
If I started hauling PA gear again, I would expect to pay 100$+ for something truly durable. Or, have nice light gear I could haul with my two wheeler.
That's a pretty lightweight 2x15!