Beware the hard cases with foam inside, they will retain moisture and eventually rust your firearm. Yes, you can use it for storage but really they are made for transportation.
Just stick a trigger lock on er and your good to go, case or no case. Plastic gun case alone however I wouldn't say meets the standards.
Silica gel packets don't last forever, come in assorted sizes(half gram and up), weights are made to cover different sizes of container and aren't exactly cheap. A half gram covers 1 l and runs about $22 per 20.
Oiling the firearm works as well and costs less in the long run.
Rice in an old sock.