Hey Josh,
Glad you got it and it fits well!
Thanks for the feedback. I can and have printed nuts and bolts, but they aren't as strong or durable as nylon bolts you'd find at the hardware store, so it was more just to see if I could.
Not sure what you mean the nut is "loose" -- I designed the stiffeners with 3mm thick ears, so they add a total of about 6mm of thickness. Used with the stock equinox bolt, it should still grab about 5-6 full turns of the nut before it snugs down, which should be plenty. If your nut/bolt is stripped or stripping out, to replace them it's all 8mm hardware. 5/16" will also fit nicely. The stock bolt is 45mm long , so ideally you'd want one 51mm long -- 2.01 inches. If your hardware store is like mine, you're more likely to find nylon bolts in inches than mm. So a 2" long 5/16" nylon bolt with matching nut would be your best bet.
Feel free to PM me if you have more questions.