It's really not worth shielding the pickup cavities when you've no way of shielding the controls. You've got humbuckers, so you really won't get much noise from them. If you were worried, then covered humbuckers would be better than tape shielding as the entire pickup is then shielded. Any noise that is picked up will come from the unshielded single wires in your wiring harness

So make your harness wires as short as possible. It's all quite compact in a 335, so it shouldn't be too big an issue. But remember that you need to run wires around the D(iamond)-hole (as it's not an F-hole) so you don't see them. The longest wire runs are from the pickups, but those cables are shielded. Where you end up running signal and ground cables in parallel, you can wrap them together so the ground cable acts as a partial shield.

And don't forget to connect up the bridge post grounding wire!