Magnus, now I've got to experiment with this too. I would think if you used linen tea bags they might work better. What steep time were you using, as an earl grey needs a
three to five minute steep just off the boil, any longer and you'll get that super bitter taste you mentioned? One possible way is to steep the tea in water normally, remove the tea bags, and then use a low simmer to evaporate off most of the water and then add that to your PG. It will still be a bit more bitter than a proper steep but shouldn't be as bitter as an extended boiling. Another way may be to go Russian and boil the heck out of it and use something like
vape Wizard to help cut the bitterness and add extra sweetener and/or a citrus like mandarin orange or lemon to help cut the bitter further. The Bergamot in the Earl Grey is going to be your main problem as it will go from tasty to terrible with a second to long of a steep. This is definitely one to ponder.