thanks @Gunner I did try a search first, there was nothing obvious other than previous problems with the contrib package i'd previously tried and some mention of using rabbitMQ with MQTT.
My understanding is that's MQTT is a different plug-in at the rabbitMQ end that allows you to use the standard MQTT nodes in node-red. Unfortunately, I have no control over the rabbitMQ end so that option is unlikely to be available.... but I'm in the process of checking that separately.