I havn't needed it for my scope yet but use a product called "Fog Off" in my breathing apparatus face mask.
It's avaliable from diving shops.
May be worth a go ?
MAD for it.
Steyr LG 110 Gary Cane, Leupold 2.5-8x36 TMR
Member of the UYK, UYB, UYC, UYH & UYE club.
I would like to agree with you....but then we would both be wrong !!