Not wishing to hijack the thread but
Phil has said that he is trying to set the new "thank you" button and still keep old the old "thank yous" but that it is proving harder to do than he thought it would be.
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What I did with my bread trays is to "paint" the top with varnish. While the varnish was still wet I poured sand on them to give the smooth side some grip.
When you use them it is no use throwing them under a spinning wheel. You have to jack the vehicle up, place the mat, lower the vehicle and then drive off very carefully.
As Old Arthur suggests, you are supposed to stop on top of them
You were lucky that you were not using PSP. I saw some d******r do that when a Land Rover got set. The PSP came out like an arrow