RE: Battery next to the engine???
Replacing the batteries isn't the concern here, it's replacing the airplane if the batteries fail. Also, I believe he was referring to heat generated by the engine being transferred to the batteries, not heat generated by current.
Anyway, I have lots of ideas on this subject, but take them for what they are worth--just ideas. Never tested.
But, you could isolate the battery box by a thin strip of rubber between the box and the mount. THen, use some high density foam surrounding the battery inside of the box. This should definitely take care of most of the vibration problem. The foam should also insulate from some of that heat, but definitely put the battery opposite of the muffler. THis would help counter-balance the muffler anyway.
Just ideas....