Most planes have the fuel tank behind the firewall. However, some planes (such as a profile plane) have the fuel tank mounted behind the engine. These tanks are normally secured with zip-ties or rubber bands. The fuel tank inside a fuse needs to be surrounded by foam to prevent the sloshing (foaming) of the fuel inside the fuel tank itself. I normally pack enough foam on all sides of the the tank to prevent any movement. You can also use a strap of some kind (as extra insurance) behind the tank to keep it from moving. Foam normally does the trick for me.

Ailerons work opposite of each other. If you look at the front of the plane from the tail and want to make a turn to the right, the aileron on the right wing will go up and the left aileron will go down. For a turn to the left, visa verse. On some planes you will have separate servos to operate the individual ailerons. If this is the case, you will need a "Y" harness to hook the two servo leads into one that goes to the receiver. Most trainers use one servo located in the wing to move both ailerons. A person at a local club or a a good hobby shop can take a look at your plane and tell you what you need (since I don't have any pics)