To do a paint job on a MEC, you need to REALLY clean it well. I tore down and repainted my 12-gauge Sizemaster before selling it. I was lucky that I had a friend with a small sandblasting booth which I used to clean up the frame. Like Flash, I did a couple of coats of Red Rustoleum and it came out nice. I'm pretty sure that the frame is cast, so can hold oils and grease, so a good cleaning is a must.
Give MEC a call. They are a great company to communicate with.