If you are making more guitars like this, then I suggest you do a search for adhesive backed neoprene foam sheets. I managed to pick up a collection of sheet sizes in the UK, and they've come in vary handy. You don't want too large a sheet of each size as you won't get through it, but I've used a mixture of sizes for propping up soapbar P90s so they are level with the guitar top and sticking underneath pickups as springs or to reduce vibrations. I had a quick look on the Aus eBay site and quickly found this http://www.ebay.co.uk/itm/neoprene-s...4AAOSwcLxYKo~r , though there are probably other suppliers. You can probably compress the neoprene foam by 1/3 to 1/2, so it gives you some latitude in the thickness you pick, but it is wise to have a selection of sizes in case you need to step down or up a thickness.