The cover comes off with some effort. The padding may have been blown in
through a hole in the steel frame as it is stuck to everything. I pulled
it out in chunks as I worked the saddle off.I enlarged the hole ,lined
it with duct tape and ran the valve through it.I used a 4.10/3.50/4
tube from a hand truck tire.When laid on the seat top it looks exactly
like a bike seat that has a relief hole.The cover goes on easily.It is
a plush,smile inducing ride.I have never used a miyata air seat so I
can’t compare. 
–
cheechee