How are you going to get shocked if you touch a totally insulated material? You aren't. You could hook up 2 live wires directly to a piece of PVC and still not get shocked. It makes absolutely no difference between the flexwatt sitting in the rack and using aluminum tape.

Think of it this way. If you have a metal rack and the flexwatt is touching it, it will transfer the electricity to the rack with or without the tape. The tape might let a little more power flow, but some will transfer regardless. This is why metal racks are usually grounded. But it isn't an issue at all with racks made of a non-conductive material.