Sorry, I've been dealing with some carPC issues. My screen had a bit of smoke emitting from the top, so I haven't made a whole lot of progress.
I'm planning on making a "false" backing that will cut a few inches of the trunk and place the amp, PC, and woofer behind it. Right now though, I just have the piece of wood I'm planning on using sitting in the trunk with the amp bolted to it.
I actually think the Mustang trunk is very respectable (for a convertible).
As for boot times with the SSD, I haven't fully tested that with final software setup. I think it's about 30 seconds from power on to music but I'm quite sure I can get that down a bit. (I'll post some times when I get it back up and running.