Wondering the trick to taking it off. I'm guessing the 2 metal bars I can feel down in the seat need to be pinched together to release the backrest? It's kinda tuff to maneuver around in there.

 

Yep ... There's a spring which keeps the two rods spread apart and located in the base bracket. Slide your had down as far as you can and give the bars a squeeze and you will be able to remove the backrest.

 

No way to get hand down behind backrest. I used a C clamp and got it out. Not sure who makes the seat it’s after market maybe that’s why I couldn’t get my hand in.