It depends on the brand of PETG. I made a license plate frame out of black/white Overture PETG a little over a year ago and it still looks just as good as the day it was printed. It has withstood two Houston summers (the recent one with 3 months of 100f+ heat) in direct sunlight with no deformation what so ever. You can also try making it out of PET-CF (not PETG-CF). This filament has an amazingly high glass transition temp. I have printed multiple items that survive 140F - 160f temps with no deformation at all. You just need to have the ability to print 300c and a bed temp of 90c for it.