The plane is a Nexstar 46 trainer ARF. Engine; OS .46 AX. The fuel tank has three lines and the tank rests in a saddle made of a rubber type material though not very thick. I am sure foam would do a better job of insulating it from the frame. However the neck of the tank makes direct contact with the firewall, through which it extends.
Removing the tank and running the engine does make sense and I will replace the lines as well.