It's funny you actually answered one of you question because you make 3D backgrounds out of the things you mentioned.
-With the eggcrate you buy from lowes or HD you measure the area you want. You use great stuff also bought in Lowes and HD and spray it down on the eggcrate. You have to wait 24 hrs before you can add the silicon which you should use brown GE 100% silicone. Avoid the chalky type. Then you can use what every substrate you want to add to the silicone. Here's a few pic to help you out... I didn't use eggcrate for this viv though
