I used trick tabs on the chassis with 3/8 foldover nuts. the uhmw is 3/4 bolted to 3/16 aluminum with 5/16" countersink screws and nylock nuts. the aluminum bolts to the chassis with socket head cap screws that the uhmw is drilled large enough to fit around.
when I used counter sink screws to bolt to the chassis through the plastic I could not keep them tight. every trip I'd have two or three missing.