Randy, Yup the seat is home brew as well.
The Sherpa seat was my first attempt at reshaping a seat. Its allday compfortable but to soft, its hard to shift your butt around on. I wish I would have raised the center so the seat was flat front to back and a little firmer. I may rework it ths winter. I have a friend that wants her seat reworked.
So I may do both at the same time.
I picked up a blue foam camp sleeping pad at wallyworld,and a can of spray contact cement. Just cut strips of the foam and glue on to the sides of the stock seat one at a time. I used a belt sander with a 50 grit belt to do the shaping. I added 5 1/2 inch strips to the sides. That sounds like alot but you remove most of each strip shaping it before you add the next. If your good with the sander you can blend the blue foam to the existing foam so the seams wont show thru the seat fabric. If suck with the sander no sweat you can get 1/4 inch smoothing foam at the upholstry shop. If you REALLY SUCK they sell 1/2 inch as well.
My second atempt was on my DR and I nailed it! Nice and firm, neutral from front to rear. I added about 1 1/2 inches of hight in the low spot of the seat. Same method small piece in the lowest spot smooth, add another and so on..
A helpful hint. Keep the rear of the seat as thin as you can. If your at stock thickness there you can cover the seat with no seams and no wierd folds on the rear of the seat. I have a cheepy swinger staple gun and it worked fine.
Or you could do the shaping then pay the man to cover it but thats no fun.
Cost about $40..depending on what fabric you pick out.