Guys,
Sorry, no flames intended, but the above statement is incorrect and should be disregarded.

The UAT instructions are very specific regarding the cap.

Quoting paragraph two on the face of the BVM instruction sheet that included in every UAT packed and ahipped by BVM:
"Apply a wrap of safety wire to the 6mm tubing on the brass fittings. Periodically check that the plastic cap is hand tight on the bottle neck."

The photograph on the front face of the instruction sheet also shows that the threaded bottle neck comes with a teflon tape wrap to help seal the bottle. Quote; "This shows the proper orientation of the sack in the tank. It is best not to open the tank unnecessarily so as not to disturb this setting. Note the teflon seal on the bottle cap threads."

If you mount the UAT in the position indicated on the instruction sheet, visible in your installation, and at the suggested 20 degree angle with the brass fittings up, it should not be much of a problem for you to occasionally check the cap for tightness, like at the first flight of the day) and the UAT for security of mounting.
Preventative mainenance checks sometimes prevent inflight problems.

These quotes are supplied for those among us that don't read the instructions.