RossMosh would palight 3mm PVC from Grimco work as a surface?
No reason why it shouldn't. Just understand that 3mm PVC is relatively thin so as said below, you may cut through it. The benefit of 3mm PVC is it's low cost and the fact you can stack it on top of each other without much thought or effort.
we did ours similar, we used .125 aluminum made it 4 x 10 and than added a 12mm PVC top. We tried the 3mm but it was too thin and was able to cut through.
Wish we could have done ours as a 5x10 but non of our suppliers carry the PVC in the 5x10, that's why we had to go with the 4x10 as we didn't want any seams
You should ALWAYS make the table larger than your intended signs. example would be banners, you have a 4x8 banner and 4x8 work table you are constantly having to shift the banner around to hem it and place grommets in it