I did this install and was told not to put the wires up. This is an air conditioned space with no exposure to the elements. Makes a much cleaner install in my camper if they are wires up.
asked
MPPT install with wires up
Violates IP certification. Air contains moisture, even more relevant with an air conditioner. Do not mount it that way. Water doesn’t flow uphill for a reason.
Wiring for convenience only causes problems.
Condensation? Humidity? Leaks?
Take your pick.
Strangely enough, most water us humans encounter originates in the air, the exception possibly being submersible installations.
That is cutting corners, and not best practice nor recommended in any form.
From the manual:
Substrate also appears somewhat flammable.
...or even just from those two large water lines that run directly through your electrical compartment.
I flipped them. 
@corn18 I replaced a mppt recently that had been mounted USD under a light.
Upon inspection it was found to be full of dead bugs. Had maggots wriggling out and smelt awful.
It took a day to scoop, shake, dry, blow the bugs out, and still ended up with a dead mppt.
Where is the water coming from? Just the air?
Water can wick along the inside of the cable's insulation from the solar array if the cabling is not sound.
