I bought some gel pad material and some foam from Walmart. The pads are from a yoga mat and a "gardening pad". They are a soft, gel-like pad with a "closed cell foam" material, so they will not absorb water.
The theory I used to make the "new pads" was sort of counter intuitive. I didn't really put any material/padding where I had a sore spot. I left that area "open" but left foam in the area around that spot to proved support and relieve the pressure point.
I used my design for a while to make sure it worked. I used some shrink wrap to attach the pad to the top of my seat while I was riding. Once I got the design I wanted, I took my old seat off and swapped out the padding.
The stock seat cover on my 07 UC was really easy to remove. Just a few staples, so a tack puller and needle nose pliers are all that is needed. I just used a staple gun with 3/8" staples to put the cover back on.
I just removed the staples to free up the padding under my portion of the seat. I left the passanger section alone. You just peel back the seat cover, then there is a plastc membrane/sheet to keep water out. Then you will see the cheap foam. It it really not hard to do. A little time shaping and snipping. The seat cover when pulled tight and stapled keeps everthing in place. Cost me $28 total.
To me the key was NOT adding padding to a sore spot. You need to lift/support the areas around it.