Any kind of oil, a lot of old farmers use old engine oil but I do think that can burn the ram's chest, so I use vegetable oil.
You want a thick gloopy paste that will coat a wooden spoon or flat stick, whatever you are using to apply it with, and stick to the wool well. Rub it well in, all over the keel and up into his chest and a little way along his belly.
The first time you do it you need a fair bit, subsequent top-ups a wooden spoonful or two should be plenty.
The powder disappears into the oil at an alarming rate and it takes way more powder than they say on the packet to make it thick enough to apply and have it stick.
So I would put about half-an-inch to an inch of powder in the bottom of whatever you are mixing it up in, then add oil slowly, stirring it around as you do so, until you have a thick gloop. If you keep it dry and covered it will keep all season, so you can use any excess for topping up.