Structurally it should be fine. Remember that the original battery was located there in factory PA 18's. Like mounting anything else, you have to use proper fabrication techniques.
But . . . . as said above, why? Boone don't get that hot (I grew up south of Lacrosse) and new avionics do not generate nearly as much heat as older models did. They are also smaller than they used to be. I have fabbed panels for certified Cubs, using the short factory panel, that had all instruments, com, and intercom. You can even fit a GPS using a ball mount. I'm assuming that you have no header tank? This means you have plenty of space between the firewall and the panel. IF YOU NEED TOO, you can mount components in this space. Some mount them on a horizontal shelf tied to the X brace behind the panel. I prefer a vertical panel tied to the structure on the backside of the firewall.
Stay with small (2 1/4") instruments and small radios such as Trig or Becker (also 2 1/4"). They take up less space and don't need trays to be installed. If you put the battery under the seat, or somewhere in this forward area, put the instruments and avionics on the panel, along with the breakers and switches, you'll use the minimum length of wire for your harnesses. Shorter runs of wire = less weight and less noise issues.
With the availability of ADS-B systems, for new installation, you shouldn't need to mount any of these items in the rear.
The one item that really should be in the aft section is the ELT. It needs to be mounted where it has the best chance of surviving the crash, even if you don't.
Web