I've built 2 cabs using those panels, I didn't use carriage bolts for the sticks (Happs on 1 cab, the other had Ultimarcs), I used pretty thin (1/8" or so) machine screws with little bolts and lock-washers on the botton, they've never budged. I did paint the screw heads black so they aren't as shiny. Carriage bolts are usually pretty thick, no? With squared-off tops? Those wouldn't work well for this unless you filed the holes in the panel to be square (unless I'm thinking of something else...) In any case, a trip to any hardware store will yield plenty of obvious options, it's pretty much a slam-dunk with those panels.