We have been doing some renovations in the kitchen and removed a microwave/hood that was mounted over the stove. My wife now wants a shelf there (it's high enough that I'm not concerned about flames). I was going to just going to build a simple wood frame, attach to cabinets on either side and to the rear wall, and top it with either MDF or a sanded plywood and then paint it all. I've never used MDF, so not sure about it. My concerns are with the moisture from boiling water and general heat. Which would I be better with?