Here is one of the threads about the seat offered by powerbypcx.
http://www.hondapcx.org/viewtopic.php?f=7&t=1401
I've had mine for a few months before I even realized that I was supposed to swap over the little weather strip that seals the seat pan to the lip of the scoot:

Anyway, thankfully I still had my seat, so I went and the old seal just peeled off very easily. Maybe the cold weather helped, but all the stickiness stayed with the rubber. I tried just pressing it into place, but it wasn't sticky enough, so on with the real glue.
First, the seat must be removed, but since you are swapping seats anyway, no big deal, right?
My first issue was that the new seat material was cut a bit long and was in the way of a clean install:

I didn't want to cut it, so I just temporarily taped it back out of the way:

The next area of business is what glue to use.
I have very good luck with this yellow contact type weather strip adhesive. This is Permatex brand, but 3M makes it and many others.
I don't like the black version even though it doesn't show up if you get a bit sloppy.
The main thing is to follow directions and let it get tacky before pressing anything together.
Normally, it would be applied to both parts, but since the strip was already sticky, I just put it in the channel sparingly using a q tip:


Once it starts getting sticky and not slimy anymore, start at one and work your way around.
I used 2 different tools to press it into the channel:


If everything goes right, you end up where you started:
