With a hot and humid climate, the ARF covering will slowly degrade over time. I know because I stay in Mumbai (Bombay) which is a typical coastal city. Later, when you take the models out for use, the covering will slowly peel off, no matter how many times you iron it down. It will not weaken the airframe in anyway as long as it is not so moist that fungus / mould begins to grow. You can always use striping tape over the edges of the trimcote to hold it in place but there is not much you can do for the basecote. Other than that, storing outside is no problem

You can store in airtight containers. Even the double box that the ARFs came in are quite good for that. I would tape over the lid as a further insurance. Thats the way I have stored the 10 odd ARFs whos turn hasnt come yet (I used the original cardboard box though). I have I wouldnt use a use a dessicant (silicon get etc) as you dont want the wood to dry up too much

Ameyam