They're in the rocker panels just fore of the rear wheels if your using a factory jacks (recommended). If you're going to use a generic floor jack, then put a piece of wood about a foot long between the jack and directly underneath of the jack ports in the rocker panels, or do the same where the rear sub frame attaches to the chassis just inside of the rocker panels, but in addition use a rubber pad and/or a folded up towel for protection against scuffing/bending something. Do one side at a time.
Jacking under the sills is a bad idea and will likely result in bent panels. I always use a trolley jack under the diff and the front cross member behind the sump. Position jack stands under the sub frame mounts. Also use these points when using a bottle jack or similar since these are the strongest points under the car.
The factory jacking points can rust out and will therefore collapse when subjected to the weight of the vehicle. However there's not many choices on a car with depressurised suspension.
My jack ports are in perfect shape and got this idea from my local shop. Jack up on the diff, put bolts the same size as the trunk jack tongue and lower bolts inserted into jack ports onto jack stands.
Gotta try this. Too tempting to remove the struts myself and shop can't have a lift tied up for 10 days while Martin rebuilds the shock struts.