If you have spray equipment - use it.
Spray is almost always better than wipe on. You will just have to work on your technique. I am not familiar with Arm-A-Seal but I'm sure it's not any different than any other urethane as far as spraying goes. It appears the rough surface is partly due to it being too thick and not flowing out, just add a little thinner and it will atomize better.
I also am not familiar with your spray equipment. If you are using a conventional spray set, 20 PSI is way too low. For urethanes I use about 45 to 50 PSI.
Maybe I could talk you into lacquer sometime. It is much easier to spray than urethane and way way faster drying.
Retired, living and cruising full-time on my boat.
Currently on the Little Tennessee River near Knoxville