I'm playing devils advocate.. =-(
UV, I don't think you will need. Why?
Well, your putting two Barra's that you have had for quite sometime. So you know they have no parasites. Even if they did I am sure you have treated them already? As you said this will strictly be your Mundi tank. and will not be introducing any new fish with these two. In addition, do not feed live. So the the UV being a parasite preventive will not be applicable to you.
How about for algae control. You stated this will be kept in doors and not in the path of direct sunlight. So algae can be controlled by amount of light kept on and should not be an issue nor would require a UV to combat the issue?
So two primary reasons you would want to install a UV would not be applicable to your needs. It will just be an added maintenance and upkeep & cost out your pocket.
Unless, your planning on plumbing your other tanks together as a central filtration system? Then yea, I could see you needing a UV for preventive measures since your always getting fish.