Dang, I need to try that. Good idea.
It might just be the specific spool/brand of PETG you used. Try buying some from a major well-known manufacturer, like Overture, Polymaker, etc. I've had cheaper brands shrink, warp, have adhesion issues, and all sorts of other quirks.
Make sure it's from one of Sunlu's official stores... aliexpressis pretty shady lol.
Nope, this is the same size as the stock Prusa sheets. The sheets are all a little bigger than the actual build area.
This is just a regular-sized Prusa MK4, 250 x 210mm xy build area. I made this custom magnetic G10 sheet for printing PETG, it's 253.8 x 241mm.
You could also mess with your retraction settings to try and reduce stringing.
I had one weird roll of PETG that could only be printed at lower temperatures, so it's possible. Still looks like the filament is wet to me... I recommend picking up a Sunlu S1 Plus when it drops under $40, I like being able to both dry the spool and print straight from the dryer (only takes a couple hours to re-absorb moisture).
Ended up moving the little 500VA UPS from my computer to the 3D printer. Hopefully it'll help for brief blips.
This model was set up for it already in the .3mf file. It stops, moves the toolhead over, automatically unloads the filament, and waits for me to yank it the rest of the way out then stick in another color. It then purges the nozzle a bit to get the main color fully flowing and asks you if it's correct before proceeding. I did this like 7 times for this stupid half-failed box lol.
Edit: Also, you can left-click the plus sign on the layer slider at any height you want after slicing in PrusaSlicer to add manual color changes in.
This could be it, OP should check what the actual temperature says on the screen during printing.
Aside from drying, here are some thoughts:
Double-check the print temperature, PETG should be about 240-ish. Also the spiral vase mode may be the issue if your model isn't designed for it. Also check your z offset, the first layer should be almost a flawless sheet... if not, stop the print and try again while live adjusting the z until it's correct. Typically PETG doesn't like to be squished down as much as PLA.
Enclosure is mostly to keep cat hair off my printer (my cat sheds like crazy) and to filter some of the microplastic dust and fumes. It does reduce warping by keeping the volume warmer than room temperature, I print a lot of PETG so this helps.