I have a low-power 4:1 toroid balun almost ready in a little plastic
box. In order to keep the rain out, I am sealing everything up, but I
am also considering space-filling materials.

I am leaning toward filling it with hot "wax" - actually, paraffin
from standard household candles, although a harder grade like
sometimes found in old military equipment should be better.

The pro should be that the box would not become sealed for eternity in
case I want to re-wire something in the future, while epoxy is bomb
proof, and urethane foam is also rather hard to remove.

Is there any electrical con to be considered?