I'll be making some of these this weekend for the sand hills trip and I'll post up pics then, but they're simple to just describe. You bolt two 1' by 4' pieces (or whatever size you want, you can glue laminate them too.) of plywood together with bolts that are longer than the thickness of the two boards by the thickness of two nuts, 2 flat washers and a lock washer. The head and flat washer go on top, the two nuts and lockwasher / flat washer go on the bottom. the more bolts you use the better, make a pattern. The nuts grab the earth, the heads grab your tires. I grew up in NYC, we wheeled the Staten Island garbage dump and beaches, also in Jersey, and we had a lot of sand. These work great and are cheap to make, and in a pinch you can use the bolts for something else or burn the boards. They span holes or cracks well too. There is a crappy commercial version called sand mats that are flexible and basically worthless, probably out of business but can give you the idea. Home Depot sells 2'x4' plywood and will cut it for you, all you need is a drill and a dream. Pics this weekend!