Here's how to make a tandem seat for a moped or motorcycle from any cushion that's roughly the right size and shape.
I got this armrest cushion from a boatyard dumpster.
I suspect the fabric is UV-resistant.
Step 1: Before
You can do it, but it's uncomfortable and probably dangerous.
Remove the seat. Ride around on the moped like that.
Believe it or not it's already greatly improved!