Dog Wheel Chair Adjustable Bracket Prototype

I was looking for an adjustable no glue attachment method for the brackets from Erica Charbonneau's FIGO Rear Support Pet Wheelchair -https://www.thingiverse.com/thing:1397964

This is what I've come up with so far. As you can see, it cracked a little at the edge when I tightened down the bolt, so it look like it might be necessary to extend the bracket a bit so the bolt hole is not so close to the edge. Other than that, it holds really well. Using the existing bolt hole designed for the strap support is nice too since it keeps the costs exactly the same.