Next I measured the batting so that it would be slightly larger than the foam. Then the fabric was cut so that it was slightly larger than the batting. Layer them in this order: fabric, batting, foam then seat base.
I started stapling on the sides and worked around to the corners. I used 3/8" staples because you need them to be long enough to hold the fabric taut (but not too long or it'll go all the way through the wood).
After lots of stapling I had a slip seat that was both comfortable and pretty to look at.