After leaving the ROV sealed up and running at my desktop for a couple of hours I was amazed about how much condensation had formed. I do live in a very humid climate (Hilo, Hawaii 105cm of rain so far this year) so I'm not surprised.
I couldn't find any individual silica packs at my local hardware store so I ended up making my own using some refill of bulk moisture absorbent and coffee filters. The coffee filters are good to use because they don't break down when they get wet.
After making a little absorber packet and putting it in the ROV I have not seen condensation forming again. Even if you don't live in a super humid environment I'd still recommend putting in some sort of moisture absorbent just to be on the safe side.