I also have one of the $78.00 5,000 BTU Wal*Mart units that I made a
stool for that straddles the opening in the front of the poptop.  My
wife, using some sort of material, made a piece that fits around said
opening and snugs against the air conditioner.  The good part is I carry
the unit in the luggage rack so there's no real hassle to set it up.
I've wondered about hanging it from a front window but haven't bothered
to fabricate anything yet.

Mike