two years is quite a long time to store ur speakers.... don't u have somebody there that could at least power them up every now and then? ur right, non-activity of your speakers may result to damage due to our humid condition even if u leave them out in the box.... m not sure if we have storage facilities here in pinas designed for ur kind of situation....
my suggestion is this, have one of ur friends use them while ur gone with the agreement that if he/she breaks it, he/she pays for it...