JennyKatz... I don't know if this would be possible on a 22, but I am planning to try one of those portable, roll-about a/c units like they sell at Sam's, Wal-Mart, etc. on my TC 255. I use those in the bedrooms of my old farmhouse and they use little current.
I am thinking the 7,000 Btu unit would fit just forward of the front dinette seat, or on the forward bunk. The 5,000 Btu units are smaller. The drain line could be run back to a bilge pump if the a/c unit was sitting low, or if it was sitting on top of the seat, it could drain overboard. I am thinking of strapping one of those units in place during the hot months, and removing it in the Fall.
The intake/exhaust is designed to go out of a window, but one might be able to install a dorade or similar vent for a more permanent installation. The bottom third of those roll-about units just houses a water collection tank, so maybe that part could be removed.
John