Two things:

First of all, I am not at all a fan of the Hot Seat Grande.  I bought one, sat in it once and decided to not install it.  It is still on the shelf in my garage and I will give it to anybody that wants it.  For my money, the Happy Bottom Seat is much more comfortable.  I pretty routinely sit for 2-3 hours straight with no discomfort. 

Secondly, I would advise against permanently mounting any seat until you have at least several hours paddling the boat.  Moving the seat forward or aft even 1/2" can have a significant impact on how your boat handles.  If you want it to track more strongly, move the seat back.  If you want the boat to be more maneuverable, move the seat forward a bit.  On my last two builds, I decided to use velcro to mount the seats so I can move them to better match the conditions that I will be paddling in.

What Mark said. I used the Creature Comfort seat in my WD12 with velcro to hold the bottom and nylon straps, cam cleats and bronze snaps to hold the back. This setup is comfortable (I've done 22 miles in one day), easily adjusted even out on the water and completely removeable for cleaning/working on the boat.

Have fun,

Laszlo

BTW, only the top photo is the seat in the WD12. The bottom 2 photos are when it was in my old pirogue, but they are the best ones I have showing the back support details.

Laszlo

   I may some day invest in a better seat, but since I'm alraedy way over budget I'm going to try the HSG, see how it fits.  I do like the idea of temporary installation with Velcro.  

Thanks Guys