Protecting bare Aluminium Bottom Metal

Seeking recommendations.
My M70 Win has bare aluminium PT&G bottom metal. Rightly or wrongly I am concerned about corrosion / oxidation occurring over time. I am wondering about protecting the metal with protective coating. I have ruled out cerracote due to potential chipping and buildup. The bottom metal fits very snugly into the stock and I would rather not have to open the inlet to fit once coated. What very durable and cost effective options are available please ? One suggestion was to aerosol apply polyurethane but I suspect this might be thin enough to wear through in time, but I am not knowledgeable enough to know for sure. Any advice / recommendations greatly appreciated. Cheers.

Check out a product called nyalic