You can use shoogoo as the toeguard thus not needing varnish (just as the case would be if you were using a toe guard. Or you can do what @sarg does when prepping bats - apply a coat of bat oil then varnish ,then add a shoogoo toeguard . This seems the best of all worlds really.
Perhaps someone can post a link, if not look up "cricketbatinfo" channel on youtube .
That new process came about because I was preparing bats for wet conditions.
I have applied shoegoo on a dry toe and batted on a wet deck and the water and dirt has got under the shoe goo and stained the toe.
So the oil goes on the toe as per a regular knocking preparation. after a week I apply a very thin layer of a clear oil based varnish to seal the toe fibres. When set the shoe goo goes on as one application.
@simonmay5 and
@Calzehbhoy may be about to confirm if the varnish worked.
You can just oil a toe if you want instead of doing all this.
Some say a thin coat of bat wax prevents water ingress applied just prior to batting on a wet deck. This is just for heavy tappers.