Letting Milk Crate rig sit on Carpet, and GPU support material question

I am building my first ETH miner out of a red milk crate like the following.

It looks like that


Also note the bottom has holes in it.

Can i put the motherboard flush on the bottom and let it sit on a carpet while it doesnt run or would static harm it? Mind you I dont plan to let it run on carpet but if I had to move it I could see my girlfriend accidently letting it sit on a carpet in teh middle of the room. If this would harm it what would you suggest I use to cover the wholes in the bottom? I have these plastic / rubber motherboard risers but they are not tall enough to get the motherboard away from the holes. A friend suggested to just leave the motherboard plastic wrap in the bottom of the box But I am not sure if that is safe.


And a 2nd question.

I planned on putting PVC pipe through the holes to let 4-5 MSI RX 480s sit on the top. Could I use metal supports instead of pvc pipe for the graphics cards to rest on? I know CPU cases are typically made out of metal, i was just wondering if the mounts for the GPUs were supposed to be non conductive like wood or pvc pipe vs metal.

Thanks for the help if this isnt the right section for such a question please let me know where it belongs.