For eight decades, the 50 Cal. ammo box has been the most widely used waterproof box for whitewater rafting. It was widely available and affordable--dare I say cheap. But in the last few years, they've been increasingly difficult to find, and as with any other shortage, the price goes up. A new gasket in an old ammo box is as good as a new ammo box.
The box I repaired has passed a submersion test, and I will take it on my next river trip with confidence. The only caveat I would add for potential buyers is that I found the installation process pretty difficult and time-consuming. After much trial and failure, I finally used a spray can of dry silicone lube on the gasket, and that allowed me to get it properly seated on the lid. Unfortunately, I'm not sure you can buy dry silicone spray anymore. I don't know if it has been banned, but it is gone from the shelves in the stores I visited in search of a new can.
If I had to install one today, I think I'd use a very light application of silicone grease. My concern about that is that it would tend to collect and keep sand, so I would use it very sparingly. After installation, I would thoroughly clean the gasket with soap and water to remove as much of the grease as possible.
One thing I don't know is whether or not the rubber used in the gasket would be harmed by petroleum-based lubricant, as most natural rubber compounds are. If the gasket is a synthetic rubber, then maybe WD--40 would be okay. A tag on the gasket stating lubricant compatibility would be helpful.
