I use 3.5 inch long wood screws to hold mine together
I had to make several of them (6) with wheels when we moved from SO CA up here to Bend, they all held up well. I recycle our old facial boards off of our house down there, 2x8. I tied them down to in floor tie downs for the car straps in my car trailer, it was a little over 850 miles one way I did use one piece of plywood on one of them on the bottom due to running out of the 2x8 boards, all the rest had longer front and rear boards to help make sure they wouldn't tip over
When I haul them in the truck I tie them down around the front and preload the back against the tail gate, 2006 ram 3500. No wheelies or sudden stop though