So what slicer are you using to do these prints? I used to print wood a few years ago and had it setup so that every few layers the temperature would go up or down a few degrees which would add darker and lighter rings as it printed
Here I have some 100% fill TPU prints with Cura (yes the prints are 30+ hours, it is for a 2 meter+ drone for a friend) and the stringing is minimal even on one of the softest materials to print.
I use a combination between Simplify3D and Cura for my printer at home (Ender 3 Pro with flexible build platform, essentially a Prusa clone). Simplify I found works real good for things needing support and such, but Cura gives me much quicker and cleaner prints. For use with TPU I use Cura only, even with printing supports. Not sure why but no matter what settings I play with I always get stringing with Simplify3D versus Cura with both PETG and TPU which are my two favorite materials to print in. I've messed with retraction settings, z-hop, temperatures, etc but Cura with just a few minor tweaks gives me great results. However to do the layer by temperature change it is best to do via Simplify3D.
Send me a message Gary, I'll show you how I do it