battery box bolt

[d staley]

wonder if any of you guys have encountered this problem. had my 2009 wake 155 winterized and in the process the battery was removed along with the plastic box that it sits in. went to install the battery and there are two bolts which hold the battery box to the fiberglass inside the storage area. it looks like there are some type of fasteners molded into the fibergass for these bolts. installed the bolts and when i went to cinch them down the rear bolt is spinning and will not tighten down all the way. appears the fastener has broken loose from the fiberglass and now i cant remove the bolt. gonna be a problem when i need to remove that battery again. any input would be appreciated thanks.