After putting this down for a little while, I did some further poking around with the controller and the transceiver chip uses RS-485 for its serial communications. So it's not quite as simple as a tx and an rx pin. This also necessitated the use of a couple of RS-485 modules for the arduino to convert the comms to something the arduino can use.
Furthermore, I'm still unsure of what the baud rate is as I seem to be able to retrieve apparently real data at a variety of bauds. I therefore thought it would be worth trying an oscilloscope to help detect the baud rate.
Using the instructions / code / app from here I managed to set up an oscilloscope using the arduino. It's certainly not perfect but it definitely appears to give some useful information.
From here it suggests measuring the shortest pulse and using a formula you can work out the baud.
I measured the shortest pulse at about 400 µs and that makes it really close to 2400 baud (allowing for errors in display and measurement).
I'm yet to test with this baud but, again, another step forwards perhaps...