Re: Rubber mounting tank, engine and tensioner?
Do not mount the engine with any resilient material (rubber) between the engine and the frame. As has been written here time and again, you are not eliminating vibration but instead transfering it to the engine mounting fasteners which can and probably will fail eventually. Any soft material used to mount the engine or chain tensioner will eventually be worn away and will allow movement resulting in fastener failure or in the case of the tensioner, disaster.
If you must use rubber use it only under the fuel tank but even then it really does little good. A good quality double sided tape will help keep the fuel tank in place or a bead of silicone adhesive will also prevent it from loosening and rotating on the top tube.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"