Chris,

Carve your seat so you're comfortable and then mount it as a temporary mount.  Adjust it until you get it to a position you're comfortable with and then you can mark it for continued temporary (but consistent) placement or mount it permanently.  I find I move mine to different positions based on my mood, paddling desire for that day (or part of a day) and several other factors, so I like keeping mine as a "non-permanent" install, personally.

As for the thickness, that's going to be very dependent upon your seated height, length of your arms, paddling style, type of paddle, and several other factors.  

I paddle a NorthBay and a couple of skin on frames.  My seat (which I switch between boats) is about 1 1/2 inches thick at the thinnest point and possibly 2 inches at the thickest (where I'm actually sitting) carved from a 3 inch thick piece of foam.

FrankP

FrankP.....what is your method of attachment? do you rely on velcro and glue the velcro to the boat and seat pad?  i was thinking i would glue my happy bottom seat to my matunuck.  would you suggest to use the velcro system?  if so,  what size velcro do you use?  about how much square inch velcro do you use?

thanks,

Dave

Thanks Frank.  I'll probably use either velcro or bronze snaps to keep the seat secured, but also easily removable.  I'm still undecided as to whether or not I'll need to fill in the V shape of the hull with wedges before mounting the seat, or whether I'll carve that shape into the seat itself.  I guess the deciding factors will be center of gravity and depth of the 'butt dimples'. 

 ~Chris

I glue the seat in with a few small dabs of shoe goo.  As far as cutting out the seat, check out http://oneoceankayaks.com/Wshophtm/kayakseat18a.htm  As far as placement, I start my backband about 2ish inches from the back of coaming and place back edge of seat under that.  Try it out and then glue it in with a few dabs of glue.  You can also use velcro...