Also remember that the Heath Cantenna had an air vent in the top lid. The mineral oil and air would expand slightly when it got real hot, and the pressure in the can had to go somewhere.

You don't want to tip one of these over on its side as a significant amount of the oil would then leak out of the valve. The carpet in my car was the unfortunate recipient of a dose of that mineral oil and that stuff does NOT clean up easily.

If you're building your own version of a Cantenna, allow for some expansion or provide an air vent. The bigger Bird loads have a rubber membrane bladder that keeps the oil well-contained yet still allows room for limited expansion and contraction.