Because I live so close to some great paddling water (about 300 yards), I built my own portage cart. Parts include 1 1/2 PVC, a "pool noodle", some steel pins with spring retainers, and a nice set of tires, that are too heavy, and too expensive. I originally found a couple of pictures on the web that gave me all of the required info. My little cart is working very well, but I have a couple of small manufacturing flaws that are resulting in a slow breakdown. The heavy wheels and my constant overloading of the cart put a lot of stress on the PVC where the retainer pins cross through, and the holes are tearing out. One day soon, it will need a serious rebuild. The cool thing is: I now know where I got the dimensions correct, and where I came up short. I just need to find a new set of wheels that are lighter in weight. This particular set actually have sealed ball bearings in the hubs. Total overkill. I just hope that it lasts until winter.