Hi Eric I have done both over insulating and under. I noticed in an HP unit the optional OCXO was near the fan and was affected by the draft. It worked much better just putting in a baffle of thin Styrofoam to redirect the air path away from the OCXO.. It was more stable.The Cardboard suggestion seems good also.In general these things are meant to be inside a chassis and not in a draft but not surrounded by another layer of insulation.However you can always try a little box of thin foam and see if it makes any difference while watching the output on a good monitor. Spectrum Analyzer or really good counter etc....if you have something that would see a small deviation. Wally KC9INK