Any info on where to buy or how to make one. Or can I just remove the back panel and bolt it there?

 

I'm talking about installing the harness to the back wall

 

search, there are plenty of topics about both of your questions..
1. there are a few places where you can get the "B Pillar Bar" from, since technically sol's dont have C Pillars..
2. You might want to research and read up on mounting harnesses.. Its not as easy as finding a spot where you can bolt it into. There is alot of safety precautions and measurements you should make before completing the installation.

 

you can buy the c-pillar bar for an eg and it will fit behind the seats and mount to the seatbelt bolts