You can never go wrong with silica gel in your case. Especially if you will be in a humid or wet environment. In short silica gel absorbs the moisture in your case which will help prevent rust, mold & water damage. It is especially important to use silica gel in a waterproof case because the case will not only keep water out, but will also keep water in.
Assuming you’re using a 40 gram silica gel canister how many do you need for your case?
1 canister protects 3 cubic feet.