Here's a seat with padding, straps and sunshade installed. The sunshade is slid up a touch in its sleeve so you can see the upper portion of the adjustable shoulder straps. All straps mount to the seat have tee-nuts from the back side for a very secure flush mount.
Here's a closeup of the sleeves for the sunshade stays, and the adjustable shoulder strap setup.
This is the seat with pads out so you can see how all straps are fastened.