Mineral oil is the usual substance used, as its clear and non smelling.

Mineral oil is what people use these days, but it is much less funny. In practice, any oil will do, although olive oil is not suggested - smells nice at first, but will break down over time.

Are pretty much all surface mounted components fine with this?

I wanted to waterproof a micro devboard by submerging it in mineral oil. I was worried the board may delaminate or components would turn to goop