if your topping lift is rubbing while sail is up it's likely set to tight, or is too heavy a line.
Also if the rigid vang isn't viable (smaller boat, say 27 foot and under), there is always a boom kicker. I've found the kicker to be a great solution to work in conjunction with a boom vang. One must remember to secure the boom with the main halyard though, because the kicker is merely to provide SOME boom support while raising sail, providing boom lift in light air, and for reefing... it's not a long term boom support, that should always be on a halyard or top lift.
I've ditched my topping lift entirely, gone to a boom kicker, and have been quite happy... I use the main halyard attached to the furthest point aft on the boom, while the sails are covered. It also provides a decent amount of lift/twist in light air.