Boat Seat Base

I was looking at this seat base.
https://www.basspro.com/SeaSense-Boat-Seat-Deck-Base/product/10203564/-1114454

The reason I wanted something more narrow and not the normal 7x7 base, was to fit between my hatches and supports that I have already built. My original plan was to have the seat further towards the top to control my TM with foot pedal. I have realized that is not enough room and the seat needs to be further back. So I will need to go between the hatches. There is roughly 5-6 inches in between.

Has anyone used this base or something similar? Is it sturdy?

If I were to mount his here, would you recommend nuts/bolts/washers through the 3/4" ply? I originally was going to use the 7x7 mount and screw through the ply and the 2x4 support studs.

Any other ideas. Here is a rough sketch. I will try and post some pics eventually.

Had one on my last build. Used lag screws through 3/4" plywood and down into the 2x2 supports. Just as study has the bigger square ones, never gave me any problems.