I have my gun safe in a sub basement and was getting minor rust on my guns. I bought one of these and have had no issues. Lifetime warranty and works great. I would definitely buy one.
If you have a safe, get a dehumidifier.
If your safe has power: https://www.amazon.com/dp/B00D8ZV2TW?ref=ppx_pop_mob_ap_share
If your safe doesn’t have power: https://www.amazon.com/dp/B000H0XFCS/ref=cm_sw_r_cp_api_glt_fabc_W5DQQBTXGHM2AEX1SC15