Hi Roger,
Years ago I insulated a double garage/temp dwelling with the sizzalation foil paper top to bottom and not long ago did the house roof with fibreglass batts..l must say the proper batts beat the foil anytime for insulating...I would go for that!. They are so easy to split down the middle for making 2 thin batts from 1 in a small cavity. Like you say make sure you don`t compress them or you will see it on your lining bowing out if its thin..make sure you wear googles and a paper mask but.....
Cheers
