you can go out and buy a 10 gallon aquarium, and it will work perfectly. some people use rubbermaid bins. you can use whatever you want that holds water really.
again, of course you can have a system that will not overflow.
the amount of water that will flood the sump in the event of a power outage, is only as much as will fall over the wall of the overflow. if the overflow surface skimmer is set at the right height, you are not going to lose much water when the power goes out. you also have to take into consideration your return, because it will want to create a back siphon when the pump goes off. a small hole drilled in the return just under the waterline will stop this.
