As you can see I use a brass fitting. I cut the end off and drill a hole in the UDS just above the top grate. If I have a second grate I do the same just above it and in line with the top inlet. I have several reasons why I do what I do. Again the beauty of the UDS is that you can fashion it however you want; personalizing it to your liking. There is nothing written in concrete that says you cannot drill a hole and be done.
I really like the added attraction and the neatness of the construction when you add a brass fitting. It also gives added protection for the wire in case some one gets tangled in it. The sharp edge on the barrel can break the sensitive wire inside that is covered by the exterior braided wire or plastic. It is just a matter of what you prefer; there is no wrong answer.