Yemm & Hart makes Military Foxhole Covers from 1/2" thick extrusion grade polyethylene (not recycled). Comments from fire control at Ft. Bragg NC: "These are the highest quality covers we have seen."
Foxhole Covers are vacuumed formed to a mold that yields a 63"O.D. cover with an 6" rise and 2" lip. Allow at least 8 weeks ship date. Other sizes and shapes are possible when the volume justifies the mold cost.