I had thought about anchor bolts. The draw back is that the bolt exerts outward pressure to hold it in place. I think that pressure will break the plastic. I have used epoxy method before. This was 20 years ago.I don't think that drilling and tapping epoxy will hold. Have you thought about using anchor bolts instead? They come in several sizes but here is just one example,
Global Industrial™ Anchor Bolt 1/2-13 x 3-3/4" - Pkg Qty 50
Global Industrial™ Anchor Bolt 1/2-13 x 3-3/4" - Pkg Qty 50. Ships in One Business Day. Buy it and Save at GlobalIndustrial.comwww.globalindustrial.com