I'm not sure about insects but it definitely "attracts" water since it is highly hygroscopic. If I were buying DME in that quantity, and I may in the future, I would put it in 5 or 6 gallon food grade plastic bucket(s) with a Gamma Seal lid(s) and perhaps a desiccant put inside with it to absorb any moisture in the air with it.
In my area I can get 5 gallon food grade plastic buckets at Lowes and gamma seal lids at Home Depot. I store all my grain in 6 gallon food grade plastic buckets I purchased off of eBay. Using the Gamma Seal lids makes these buckets watertight and airtight so no pests can get in.