HI Crash,
My Great Planes Cap with an OS .70 cowl-enclosed doens't have any cooling problems. I have opened up both sides of the cowl nose area as in the full scale, made a hole for the cylinder head that is big enough for the glow driver and a hole for the high speed adjustment needle. The exhaust area is just a moderately sized semi-circle that allows the exhaust pipe/muffler to just barely exit. I had a rubber exhaust extension attached to the 4 stroke but that only lasted for about 7 flights before burning off. I haven't bothered to replace it. Many recommend that the exhaust holes for cooling are 2times the area of the intake holes. I can't really say that they do in this case. Here is a photo, but unforunately it doesn't show the exhaust area. Hope this helps.