It's now time to pad the seat base... Although it is hard to get and expensive, I use 2" consolidated foam. It has "spring" so is much more comfy than plain foam and does not flatten with time . Amount used for this seat cost about $35.
Marking foam with texta. I add about 3mm to all edges to allow for slight compression when gluing. Once all foam is stcuk on and shaped, I will glue on some soft 1/2" foam to smooth it all and give soft initial feel. I cut foam on bandsaw, but you can do it with a sharp knife.. Stay-sharp serated knife works well, but you need to gently pull surfaces apart as you cut, so it doesn't grip and cut crooked......
Grinding depressions for seat back lock and front catch. Wear a respirator when griding or you will quickly have trouble breathing and end up with scratchy lungs and blocked nose...
Gluing pieces to base... I use Quick Grip which I think sticks better than Gel Grip. Coat both surfaces (2" around edges is wide enough) and allow to go tacky.
Then put together edges beginning at one end. Middle will find its own place. Take it carefully as once stuck it is hard to pull apart. Once all surfaces of a piece are together, pound them with your fist or a rubber mallet to ensure a strond bond.
All foam blocks stuck together. Note that seat pad compresses when you sit on it, so don't glue bottom surface of back piece to part on which you sit, or it will reduce springiness and therefore comfort of seat.
Lines around edges are guides for rounding edges. Rider seat back will be reduced in thickness (using knife) along marked line. Multiple parallel lines are guides for shaping riderbackrest so it does not push onto front of passenger's thighs... I do shaping with angle grinder. Practice on a piece first as it requires some dexterity and an awareness of which way blade is spinning. Angle grinder will "dig in" if you are not careful.... Be patient and take it slowly and purposefully...
Once edges were rounded, I sat on rider's seat and found that front edges dug into inside of thighs. You can see the remains of two guide lines used to guide me in removing extra foam where it was cutting in. I did the same check on the rear seat...
Trimming seat back. Had to hold the camera in my left hand , but it would normally be prizing the foam apart as it was being cut.
Finished seat padding awaiting some 1/2" foam followed by plastic to prevent entry of water when riding in the rain. Remember, stitching is not water tight...