I wrap mine in wax paper first then in small airtight container so there is not a lot of air space (less chance of condensation build up) and as said it will keep for quite some time. I have never kept it for 6 months but up to about 3. Just check it every now and again for moisture and blot excess with paper towel.
DO NOT FREEZE SILKWORM FOOD. If you freeze it after its been made up, then defrost it the food will loose its cheese like consistency and will crumble into a mess when you try and feed it. This is becuase the water in the mix expands when frozen.