Replacing your carpet with a rubber or plastic liner is a recipe for rust. Dirt always will find its way in under your liner, and so will water. The dirt will grind away your paint, and the water won't evaporate well under a rubber liner.
Many people get Rhino lining, or a similar DIY liner (herculiner, rustoleum bedliner, etc).
That way you can sweep and/or hose out your interior. (This is on my to-do list