I’m confused. I think NebNorse is talking about heat creep on the Dual V2 and JoeBowler300 is talking about the Dual V3.
While both the V2 and the V3 can suffer from heat creep, the reasons and possible solutions are very different. On the V2, the two extruders are separate each with its own (IMO, inadequate) cooling fan. One solution is documented in https://forum.lulzbot.com/t/dual-extruder-v2-heat-block-fan-upgrade/3366/1
On the V3, the shared heatsink with, IMO, poorly engineered cooling flow, has a solution that works for me at https://www.thingiverse.com/thing:3213878. I was able to get the stock fan to attach with some careful rerouting of the existing wiring. There are also higher CFM 40mm fans that can be used if necessary.