TIZBAD;

First off, if you want some help try giving us as many details as possible so that we can have a better understanding of the problem (we cannot see your AC),

Secondly, try reading your post before you hit the send key - I've read your post 5 times and am still not sure what you're talking about, watch for typos and explain your problem clearly.

General information;
Fuel tanks are cheap buy a good one that fits the space available.

If a fuel tank will only fit in sideways- this is not a problem - rotate the stopper 90 degrees to keep the vent at the top of the tank. Be sure that the Clunk is still free to move about without hitting the rear of the tank. If the vent is hitting the top of the tank - trim it and put a knotch in the top of the vent line, this will prevent any vapour locks.

Depending on the design of the AC it is necessary to put the fuel tank in cap first, if you have already cut the fuel lines this can get tricky. I leave the lines long until the tank is in place and then cut them to length.

Packing material should be placed around the tank to prevent it from moving - BUT - do not pack it so tightly that all of the engine vibration is transferred to the tank - this causes the fuel to foam and the engine will shut down from fuel starvation.

Good Luck!