you'll get condensation in a keezer, no way around it. how much you get is a function of how humid the atmosphere is, how often you open the lid, etc. i've tried the 'wireless' dehumidifiers and found them to not be that great. they would saturate quickly and take forever to dry out when plugged in. could be a size issue though, not enough units. they are pricey so i went with a couple of the silica bead 'bags' in cardboard boxes. these work better and dry out in the oven after just a few hours. i recharge them once a month but could probably do it more frequently. i haven't tried the damp rid but assume it does the same thing, just don't like the idea of throwing it out and having to buy new.
be sure you have some fans moving air around in the keezer. not only will it help with keeping the volume a constant temperature but it also moves humid air around to the dehumidification product, helps keep it dry.
the kegs, co2 and beer/gas lines form a sealed system so it isn't the end of the world if you get a little funk in there but better to avoid if possible. i've resigned myself to once a year pulling all the kegs out and giving the keezer internal a good scrub down. stagnant water, spilled beer, etc. eventually should be cleaned up.
