I once had a similar setup in a closet for clones...multi levels.
I found watering in a short height clearance to be a problem.
2 solutions I found that helped was using hose with a metal tube long enough to reach to the back wall of the clones or to install the clones on a tray that can slide out of the 'box' like a drawer...then slide it back in when done watering or whatever.
I also used gravity to my advantage...sit the jug of water on top of the 'box' and with a hose + metal tube you can water easily and just kink the hose between watering each clone to not make a mess of water going everywhere.