I'm not sure if you have already installed your tray but here is a a link to my previous install. I had a 2003 TR-185 several years ago and a I added a tray. If you go down to post #7, I included some photos. I used "pegboard" type material to make a template of the cut out then I made a template of the "side" of the tray so I knew how far to cut down. I wanted the tray to sit on top of the center brace for added support. I used a Harborfreight "Multimaster" tool cut out everything and it worked very well.

https://www.bbcboards.net/showthread.php?t=584084