I think you worry too much, I have Hunted with my MLer in the Rain for days, in the extreme cold -0 and then bring my MLer into my warm truck, home where it's warm and then back into the cold truck untill it warms up, then back out into the -0 temps and back to the cold truck and warmed up then to the warm house back to the cold then warm truck out into the -0 cold again. I never had a problem with condensation, rust or the MLer not firing. I have said this a hundred times, I cover the end of my Barrel with a piece of Masking Tape, this keeps out moisture, rain and snow. If you dont get any of this in your barrel then you wont have any of these problems. I have done this for years, if you keep your barrel uncovered then it's your fault, try what I do and you'll thank me.
(BP)