Weevils adore malted grain. After emptying a bin, I give it a good napisan wash, rinse and air dry in the sun. I try and avoid mixing up grains, just to ensure that if weevils are infesting a bag, it doesn't get transferred onto the next bag. Any suspect grain is quarantined and used as soon as possible. Have not had a problem, but have read about brewers opening sacks and moths flying out.
Also, when storing grain, I write using text on the top of the bag the type of grain, the source and the date. With small specialty bags in plastic, texta can rub off, so either use a sticker if the bag is sealed, or slip a bit of paper in with the grain details. Same with hops.
Determined mice and rats can make short work of your plastic bins, so don't encourage them. Avoid spilling any grain.