Hi, I took my sheer bolts out by using a small file to grind two flats on either side of the domed head and then tapped an 11mm open spanner on to the head. The bolts un-screwed without any problems and didn't require any un-due bashing with a hammer and chissel, so no risk of damage. It took about 5 mins per bolt.
1988 1.9ltr DG Hightop refitted camper. We call her Esmewelder.