The open exhaust lets more gunk, metal and heat out while you are running it. You are only going to be running it for 20, two minute runs to heat cycle it , if I remember the instructions correctly, so that should not be too annoying. This may sound silly, but try to find the biggest plastic tub you can find, and see if it will fit over your whole rig. Once engine is running and needle set, just cover it up. At two minutes, take it off and shut it down to cool. Or take it to your flying field and get your runs in between your flights.
Type at you later,
Dan McEntee