Congrats on the purchase. I'm sure you'll like it. It's a very solid and versatile trailer - I've hauled quads, bikes and snowmobiles - all without an issue.

Good question. Here's what I did. I went to the hardware store and bought (4) ~2' length of galvanized chain along with a link coupler. If you look under the deck, there are two main beam/supports running front-to-back directly under the deck, under the center of where both machines would sit if sidexside on the deck. I simply made a chain loop around each beam, front and back. I then use those loops for hooking the tiedown straps too. It's much more secure (IMO) than the Triton 'D'-hooks they sell that slide into the deck channels and much, much cheaper. Pic below showing the back, front is the same. You can also see the other mod I did to the trailer deck up front -- used 4x4" pressure treated lumber to make a wheel stop (safety when loading the quads).