Generally a large capacity fuel tank like a 22-gallon plastic fuel tank will be installed with hold-down clamps or straps or chocks that will stop the tank from moving or sliding, and a mat is not necessary to hold the tank in place or to prevent abrasion between the tank and the deck from the tank moving around.
Using a mat will probably tend to help collect debris and dirt around the tank and retain water.
See a prior discussion on this topic at:
On-deck fuel tank padhttps://continuouswave.com/ubb/Forum1/HTML/022233.htmlThe term “mat” is nebulous. To judge the efficacy of a “mat” is difficult without knowing the material composition of the “mat.”