@Graham I knew there'd be a few fellow printer nerds on here.. I think you're right on the money about PETG. I've bee working my tune for a few weeks now.
Printing has been my obsession while taking a break from mopeds.
For PETG, I use a buildtak heated bed, too much extruder heat, and a lot of cooling fan to help with layer adhesion. Usually means running some coast and extra retraction. Running .8 nozzle with .4 layers. I've also used really soft TPU for carb/airbox booties and it works great.
Here's a pic of my modified duct on the Titan extruder. I'm a firm believer that high heat and fast cooling makes for a strong part