My MB-339 has the tanks located under the wing and they were installed in a way that you can take them out easily if you want. Since day one, it was flown withe the tanks installed.

This past weekend, I noticed that one of the tanks was a little bit loose so we decided to take them out. WOW...... what a change in the plane. With the tanks installed, my MB-339 has the tendency to drop a little bit the nose when turning and you need to work more with the radio to keep flying at the same level. Now and without the tanks, the airplane doesn't drop the nose and it's so easy to keep in a level flight even during a tight turn. The only downside to this, is that now it is more difficult to slow down the plane for landing.

My decision ? To take out the tanks and leave the plane without them for future flights. For shows, for sure the plane looks nicer with the tanks installed.

All of this to tell you that you should try to make them detachable so that you can use them whenever you want. Try flying you plane with and without them to see if there are any noticeable differences and go from there.