: If your intended use is relatively smooth surfaces and short distances, such
: as ferry loading, then smaller more packable wheels may work fine. And,
: the consequences of failure are not too horrific. If you want to move a
: loaded boat over uneven ground for any distance, I would worry more about
: strength and usability and less about the aesthetics of deck loads.
Actually, I have designed and built my own!! 
It folds into a neat little package and slips into a nylon bag that fits (wheels and all) into either of my hatches.
The design is quite ingenious if I do say so myself. There are only two parts to the cart and then the wheels with washers and spring clips to hold them. The main part unfolds and then the second part slips in to hold it all together.
It takes about 30 seconds to set it up or stow it away. Everything is welded so there is no chance of losing important pieces. I estimate it will hold about 300+ pounds.
If anyone is interested in seeing it in operation I will take a digital video of me setting it up and stowing it away.
Ian
