Hi AlohaDan
This conversion cart is 600 lb capacity. Don’t think I would ever need a heaver one.
The main reasons for the cart is A. The largest pneumatic tires possible (width and height). B. Light weight but heavy duty C. Ability to handle multiple kayaks. D. Cost and ease of construction.
This is not the cats meow but a compromise. There are some good carts out there at a price. This is an alternative. Hobie is still working on their carts to make them heavy duty. They have a tire conversion for the standard cart which is much better over rocks. If I had the standard cart and only the Hobie to transport I would be using the new tires and add a strap.
If I only had the Hobie and no cart I would go for the Hobie Heavy Duty Cart like Booligal and put up with it twisting at times.
Mine works better for my multiple kayaks but down the road I will have to replace the axel and it would be awkward to take it with me if I so desired.
The undercarriage, if faced the right way, goes over rocks and curbs with ease after all it’s a hand truck and made for rough terrain. If you were to back up however it may hang on the framework. The undercarriage can be cut to your desired configuration but I wished to have mine stand flatter to assist with loading.
Hope this helps and please note this is still only a compromise.