I'd cut away the rubber washers and use silicone between the taps and bath on the top side. You'll be able to remove them in future if need be, I've not had any real problem getting siliconed basin wastes out for example. Silicone remover is a godsend in such circumstances.
You don't need any ptfe on the backnut threads. The silicone will help stop the taps rotating if you have trouble tightening the plastic backnuts enough given the limited space.
Of course opinions may vary!
You don't need any ptfe on the backnut threads. The silicone will help stop the taps rotating if you have trouble tightening the plastic backnuts enough given the limited space.
Of course opinions may vary!