No, but it fills in the bend in the headrest behind my neck:Will it check your blood pressure?
I was thinking about the seat pan... Looks possible for neckrest. Review?
It looks pretty durable, so I don't think UV will be a problem, especially under your headrest pad.How salt uv resistant is the pad. Does it hold pressure well and conform.
If someone could engineer a hinge mechanize to use one of those bags to change seat recline on the fly you'd really have something. Raise the seat for hill climbing = more power. Then drop the seat for the flats = more aero.