Visit my web site and look under installs. You'll see the exact installation albeit with an FT40 Yaesu.
In reality, the AH-4 is very rugged, and I have not heard anyone who ever had any problems no matter where they mounted it. The only consideration with respect to the AH-4 is the cable packing nuts. They do not seal tight and moisture can get in. This means you should install it with the packing nuts down, and make some provision to protect it from direct spray.
Incidentally, several of the SGC models can actually be immersed without damage if the seals are in place. For more information, visit my web site and look under Antennas.