DIY Menthol: 2/3 crushed menthol crystals to 1/3 PG in 10ml bottle. DO shake this gently until the crystals dissolve, or just leave it overnight, and shake it slightly the next day.
Do Not heat steep this!! It will crystalize the menthol. DO shake the stuffing outta the final mix , let it settle and you're good to go.

Also, mix should be less than max VG. 70/30 seems to work best.