Fold down rear seat brackets??

To still use a fold down rear seat with a mini tub, you need just make a block thick enough that your seat can bolt too, AND still be able to fold down which is pretty thick. You can just put (2) tapped holes in each block then thru bolt them from the inside on the wheel tub. But that will place your seat back at a weird angle.

To not have the seat back at a weird angle, takes more thinking...
You most likely will have to make an articulated bracket made out of (2) pieces that relocates the pivot point lower, but then your seat won't fold exactly flat on the lower cushion...

You actually need a bracket that lowers the pivot point and then has more articulation to lay flat on the lower cushion.

Have fun!