Hi there,
i had the mount break on my 04 , i just had it welded again , i also packed some thin neoprene around in the box or around the battery, and never had problem since.
I sometimes think the battery needs a touch of clearance around it in the battery box, to allow the mud and debis to be cleaned from around it at times,but then your going to get slight movement in there also which can maybe fatigue the rear bracket on the box,Check that the rubber securing the battery down does not allow it to bounce in the box also.
you maybe able to glue in some more rubber, from something like a old bicycle tube, to reduce some of the movement in the mount , or just replace it with a new one.
Regards,