Wine cellar dilemma

[CRHUTCH1951]

3 years ago I moved into a new house. The basement was not finished so I built a wine cellar using one of the corners. Two walls are below ground. The two other walls and the ceiling I had insulated to R32 and used water resistant sheet rock. After which I tiled all the walls, used cork tiles for the ceiling and put an old-world cobble stone floor. The room is is 920 cubic feet and I have about 400 bottles. I meant this to be a passive cellar. For most of the year the temperature stays at 58 degrees with 60% humidity. However for three months in summer the temperature creeps up to 68 degrees. I am trying to figure out a solution. I am thinking about purchasing a inexpensive self-contained cooling unit to use just during the summer months. The unit I am looking at is the KoolR Magnum. Wondering what y'all think. Thanks.