In the end I ran out of time this week so had to cheat a little and use liquid smoke. I cooked it at 110°C in the oven after coating with the smoke.
It actually turned out pretty well - the sous vide method has left really juicy tender meat, much better than previous salt beef attempts I’ve done using traditional methods.
flavour was ok, a bit of the sweet side so I’d reduce the sugar content substantially next time.
Not the most artful of pictures but you can see the colour was a nice deep red.