I used a similar method, actually, for a few years. Then I got Corky's mount. When I removed the straps I noticed they had become very hard and brittle feeling. This was with the battery located in the front. I imagine the process would be accelerated in the back due to heat. FYI.I'm sure someone is going to call this ghetto but its worked for years and passed SCCA solo national event tech inspection, use a ratchet strap from Lowes and ratchet it around the battery and the tray, here is how it looks in a mk2 (excuse ghetto camera pic)
There are other fancier ways of just using shorter J hooks, etc. You don't need a different tray but just different mounting methods. Posting pics of how your battery sits in the tray will help determine a good way to mount it. I like this way though because it is fast, easy, cheap and effective. I guess it doesn't look the best though.