With MDF, the connection can't get much stronger than wood glue and screws...
If by putty stick you mean epoxy, it'll work, but epoxy is best for gluing oily woods or dissimilar materials in my experiences. Gluing non oily wood is a non issue if using wood glue as the bond is stronger than the wood itself.
What are your Balusts made of?
BTW, I like you cab design. Looks great.