Phil - you unknowingly replied to a topic about a Despatch oven about a year ago: Automation Professionals' Advanced Modbus Driver - #22 by pturmel
The issue we found with the Protocol 3 is that it uses Function code 23 to edit profiles - I believe you added functionality in your Modbus module.
We ended up specifying Watlow F4T controllers on new Despatch ovens. The costs are a bit more than the Protocol 3 but the engineering hours saved in working with the Modbus protocol is definitely worth it.