I use that trainer but didn't have a CG problem, I moved the gear around and got the CG. The plane is designed to have the engine upright so the exhaust tends to slather the top of the tail feathers even when using a deflector. Just clean the covering really good with acetone then use the sticky weights on the stab close to the fin like John mentioned. I wouldn't worry too much about top or bottom on this plane but as John mentioned, over time the oil can remove the sticky on the weights but if they are down on the covering real tight it will take a very long time. When I was first given this plane it had a Magnum .91fs engine and I changed to an OS .91fs. The only problem I have had is getting a good fuel tank location. It's a nice flying plane and I have taught several students with it. It's so old and used now parts have fallen off of it and it still flies well.