I have the same issue, the main issues I believe are that the garage has no insulation above it, it faces west (the setting sun makes it unbearable), and there is no air conditioning. I am looking to start with putting just some R-13 roll in insulation and see how much the temps drop. I've already insulated the garage door with a kit designed to do it.

My cabinet is going to be the same size as well. Any help would be greatly appreceated.