Were I to attach anything, I would use the "bottom" reinforcing plate - the space left and right to the "stand" lock.
That way you would not penetrate the vacuum chamber and the bottom is also pretty stiff as it has re-inforcing ribs. You can also put "backing" plastic washers from behind to spread the load etc.
Also, the hose connection is pretty strong on itself and can be very stiff when pushed in. Relying just on that may not be such a bad idea ... Not sure if you have a CT on hand, but the bag can be removed with the hose plugged, so there is no issue having something press-fit in the standard hose hole on a permanent basis.
Those holes are for no accessory anymore even in Europe. For sure, they were not for any fixture given these are just punched holes through the plastic with no reinforcement. The metal plates behind are grounded electrical contacts so they may have been (planned)
for some accessory that would provide the electrical ground from the CT with the holes needed to reach the contacts. May hvae been useful when Festool was shooting for the Car workshop market. They are definitely not meant for any mechanical fixture.
