As 66% isn't terribly high, I think you can get it down further without needing to spend a ton. I think one or two of the rechargeable silica gel products, such as the Eva Dry, will bring the humidity down substantially. You may need more than one depending on the safe size. I tend to favor these myself given they do not require a power source or a lithium power cell, and they physically store the liquid, which causes the coloration to change in order to notify you when a recharge is needed. The only downside is that once that type of product has absorbed a certain amount of moisture, it will not do a thing until it is recharged.
Putting a standard dehumidifier in your basement will help some, BUT, this still may not solve your problem. While I am not sure of the exact material Liberty uses, the fire material in your safe likely has a high water content. If you are not constantly opening the safe, then humidity can accumulate inside even if the surrounding area is kept dry.
I have come to personally prefer to use a product like Corrosion X on most of my firearms inside of safes as a secondary backup. The product I was using before was child's play compared to Corrosion X, which can protect very rust-prone metals from rust for months upon end in 100% humidity.
Putting a standard dehumidifier in your basement will help some, BUT, this still may not solve your problem. While I am not sure of the exact material Liberty uses, the fire material in your safe likely has a high water content. If you are not constantly opening the safe, then humidity can accumulate inside even if the surrounding area is kept dry.
I have come to personally prefer to use a product like Corrosion X on most of my firearms inside of safes as a secondary backup. The product I was using before was child's play compared to Corrosion X, which can protect very rust-prone metals from rust for months upon end in 100% humidity.