Basically all you need to do is wrap the tank in foam (I put a couple of rubber band around mine just to hold the foam in place) and then slide it into place in the fuse. Ususally there is nothing to hold the tank as it fits in pretty tight. Plus the fuel line from the tank to the carb helps to hold it in place.

Follow the directions for the fuel tank. Depending on the manufacturer, you should find the tank, a rubber stopper, a plastic back plate, a front plate, a metal clunk, a short piece of fuel line and 2 brass tubes.

Again, depending on the manufactuer, you want to line up the rubber stopper so that only 2 holes are available (1 accepts the brass tubing for the carb and the other goes to the muffler). Insert 1 of the brass tubes into the front plate, rubber stopper and back plate far enough to get the fuel line attached to it. Measure and cut the fuel line according to the instructions. Attache the fuel line to the brass tube and to the metal clunk. Look into the tank from the outside and make sure that the clunk is as far back into the tank as possible and will move without hanging up on the back wall of the tank.

Once you get that figured out, you can very carefully cut the front of the brass tube to whatever length you choose making sure that you have enough to attach the fuel line to the carb.

The second brass tube needs to be worked into the stopper and both plates like the first one was being very careful not to rip or gouge the rubber stopper. Once you get a small piece of the brass tubing exposed on the back side of the stopper setup, very carefully and very gently bend the tubing up to about a 45deg bend. Again be very careful bending the tube or it will collapse where you are trying to bend it.

Once you have it bent, slide the whole stopper setup into the tank and by holding the tank up to a bright light, make sure that the bent tube is as high as possible without touching the top of the fuel tank.

Then you can cut the front of the tube to whatever length you choose making sure that there is enough of the brass tubing to attach fuel line from the tank to the nipple on the muffler of your engine.

If you are going to use the tank from you Alpha and it has survived a crash, make sure that the Alpha tank does not leak, does not have cracks or anything else that would cause it to leak. If the tank is good and it will fit your cub, then by all means use it. Hopefully you remembered to fuel-proof the engine and tank areas of the new cub before installing the and engine mounts. Also, I hope that you have checked all possible joints of your ARF to make sure that they are good solid joints - especially at the firewall (sometimes the glue used on ARF's is not the best in the world and neither are the joints) and reinforce where necessary.

I hope that this helps you with your fuel tank question(s) and hope you have good luck with your new cub.

Happy New Year,