Wot e said!
No.1 son did a few different size holes on some test pieces and found the size that held the ones i had nice and tight as i can't remember where they came from (they're either recycled VW or MR2) so i didn't use adhesive.
Then when it's covered you just press through in the right places and it works a treat.
As far as holding it all together, i held the foam and front of the fabric in place with spray adhesive so that it doesn't all move around and then used a staple gun and contact adhesive to stick it to the back.
I used that approach for the interior of er' camper and it's held up to a few years of heavy use from the kids, so it's probaly overkill for this but was good fun to do