I made a flow that can communicate with 4 UDC's simultaneously, it does read writes to almost every register (FC20 not supported in contrib modbus), it logs to MySQL, it has a historian, and it uses Twilio to send alarms. I setup Open-VPN and put it on a 4g router and control it from my phone. This allows not only remote monitoring but remote-CONTROL. So any heat process I can remotely monitor and control, GREAT! People are afraid to touch it, too many security concerns. So now its my labor of love that I have to abandon or set-free. I have tested it in the field for over a year: it is solid. Ive been running more than one of them on beagleboneblacks and the platform is solid. I'll gladly post it here once uploads unlock so that others can learn from all the modbus nightmares and maybe even use it for their own system or find errors I missed. I know there is demand for such things and this is a really common temperature controller. I hope you all can use it or modify it to solve some other control/monitoring issues you may have with modbusTCP devices. Thanks.
Here is a drive link: https://drive.google.com/file/d/1-9l_keTZzQR9nCtsvS8fkyls9lw_7vA-/view?usp=sharing
I'll upload it directly here when my uploads unlock (just moved here from the google group).