I had a Hobbico plane with the rubber trim on the tank mount. At the risk of stating the obvious, make sure your control rods are above or below the tank in the round cut-outs. I remember thinking that my tank was not going to fit and I ended up with a very nice tight fit. I remember soaking the tank in hot water to soften it. I'm not sure if that worked or if I used the heat gun next to soften the rubber and the tank before it went in.
Dave