Lots of work, so read all the way through before starting.
Go buy carriage bolts to fill the holes in your harware (handles, rail adapter etc.) carriage bolts have round domeshaped heads with a square shoulder to keep them from spinning in a properly shaped hole.
drill holes to fit carriage bolts. use a small triangular or flat file to make the holes square, take your time so that the carriage bolts press in nicely with as little play as possible.
Play with different sized innertubes, i use one 16 inch in a single layer with no pillow. others have had better luck with other combos, so see what works for you. stretchy medical type tape will help hold your tube in place on the seat base and assist in shaping it to better fit your precious bits and peices.
don’t use alot of air, you can drill a hole in the seat base to accomodate you tubes valve to play with different amounts of pressure.
1 put all carraige bolts in place. use tape or glue to keep them from falling out.
2 Set tube (with or without pillow) in place. use tape if you find it needed.
3 put cover over seat. cutting propper holes for handle bolts to pass through.
4 put your handles and your reinforcer plate on, tug on the cover to keep things tight and shaply.
5 attach assembeled seat to uni using adapter or whatever seatpost you have.
Step six- eight, this is important, so pay attention.
6 sit on uni and ride. get really pissed off that your ridiculously expensive seat feels like crap.
7 take the thing apart and put it back together thirty or forty times until it feels only slightly less comfortable than a thrity dollar velo seat.
8 smile and bask in your underdeveloped overpriced custom seat.
Disclaimer: step six is described as experienced by me. maybe i just suck, but it took me forever to get my custom seat to feel like anything i’d want to ride. it now sits on a shelf. I use my first seat, a KH all the time with no complaints.
but my carbon masterpeice is light and pretty, just like a paper wieght should be.