On the back, I put a hook on the sway bar and anchor to the outside edge of the trailer outside the front wheel. On the front, I loop hook around the bumper base and anchor on outside edge of trailer outside the back wheel. I do this on each side and it works great. My machines stay more secure this way than using the tire straps.
I agree with Bullseye on using the trailer for other stuff (like my tractor or construction materials). Plus, you are putting all your faith in two non-bolted screws that hold one board down to the trailer cross member at each wheel. I do use E-Track, but I run it across perpendicular to the length of the trailer. I put one bolt through each board with nut and washer on bottom side so all the boards are tied together. I also put a lag screw down in every other hole that does not span a gap between boards. Since the boards are treated, the hardware has to be stainless. Cost me a few hundred bucks in bolts, nuts, washers and lags. But I don't worry about it at all. Incidentally, I just traded my utility trailer for a longer car hauler that has welded on D-rings that I'll be using in the far front and far back. I am also going to use stake pocket D-rings for the mid point between machines. Still installed the E-track on this one (front, middle of wheel wells and back), but it will probably be used for securing other stuff like lumber.