Medium duty repairs are a crazy jump from light duty stuff in my experience. We have several 4300 Durastars we run in our fleet, the first time I got a bill for "routine" repairs my eyes nearly came out of my head.
Hammerhead makes a salient point. Know what running these trucks costs you versus outsourcing so you can make a complete decision. We know that our 18t boom truck costs us about a $70/hr premium over outsourcing to a crane company. However we can justify this through the prevented downtime. Each hour that a crew spends idle waiting for a boom to arrive to bring up forgotten materials and equipment also has a cost.