I built an addition to my layout. On top of the 1/4 plywood top of the bench work I adhered 1/2 inch green insulation board from Lowes. I had to cut and piece it together to cover the entire surface of the plywood. I secured the various pieces of green insulation board to the plywood with Liquid Nails. What has anyone used to fill in the gaps between pieces of green insulation so that it does not like I have fault lines on the layout? I was thinking of using spackling. Has anyone used anything else that worked well?