Since I really have no experiance using bass flies, I won't make any suggestions on equipment. The few occasions I do go warm water fishing I usually just use streamers (most of the warm water species in RI are quite small & I haven't gotten the urge to start tying bass flies yet).

As far as picking up a new way to casting, it may take awhile to get comfortable using a style that is different from what you are used too. You may never get used to it but I wouldn't give up trying, you never know you may come to prefer it.

As others have said, if you arm gets tired after an hour take a break. If you push to hard the first hour your fishing your arm will be junk the rest of the day. I also suggest pacing yourself better as well, take a little more time between cast.

A final suggestion is if your shoulder bothers you from injuries and wear from younger days you might want to talk to your doctor. He/she might not be able to do anything medicly for you but he/she may be able to help you find some exercises to strengthen you shoulder and to loosen your shoulder before you start fishing.