Waterproofing the 1/8" thick exposed plywood

On the inside wall area of the outside kitchen, pass though storage compartment and propane tank areas of my 5th Wheel, there is exposed plywood or paneling type material. The most concerning would be where the propane tanks are mounted because it's open underneath and spray will get in there if traveling when it's raining or there's wet roads. Sooner rather than later it will rot. I'd like to avoid that before it starts. Any ideas what I should do to protect it?