Nice job on the brackets.Yes you can mount it to a warrior trike. It isn't that hard.
I have such a seat and it sits good. I have a pad for it, but I will get an other one that is a bit thicker and is more open so it breathes more.
You can use it without, but the pad ads confort.
I made these, to mount it to the frame.
I will mount it with m6 round head bolds and I will ad done rubber in between the seat and the metal. Than it follows the shape of the seat better.
My seat will be adjustable.