We use a blanket on the bench seats - we rather like the seat material in the T6 Cali and didn't want to cover it up.
Our last Cali had waterproof VW covers and fitted black carpets - it just looked a bit dull. So this time around we're using nice blankets for the bench seat and rugs for the floor. Looks far more homely and it easier to clean (well the floor is anyway!). But the front seats were impossible to cover and in a Cali you need to tread on them to get upstairs so they did get a few marks on them in Spain. Just about washed out but decided covers were essential. But again we wanted nicer looking covers so went the custom route instead. I hope they're okay because they're just under £300!