I agree with Mario that we don't need to soak our sides but that doesn't mean that people don't do it. Charlie Hoffman has been building for many years and as far as I know, he still soaks/boils his sides. When I toured the Vancouver Larrivee plant back in 1993 they were steaming their sides in a steam box before putting them on the heated bending form. In "Clapton's guitar" it is noted that Wayne Henderson also soaks/boils his sides in some sort of trough before putting them on his light bulb fox style bender.
I honestly don't think it really matters as long as the side is left to dry at a moderate rate. If the side is supported along its entire length on both sides I don't think you'll get cupping as the moisture leaves the wood.
Having said all this, I've traded in my stainless trough that I used to soak/boil my sides in for a little spray bottle. Both have worked fine for me.
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