I feel like the date flavor would make an exciting and delicious contribution to a Dubbel. I have never tasted or used it though. I would suggest that you experiment in a split batch by using a date syrup and no date syrup, or something similar to get a good taste for what it contributes.
Good...
I built two keggles from decommissioned kegs. They were heavy and a PITA to clean. Upgraded to a couple 16 gallon Bayou Classic kettles and totally glad I did.