Consider getting a rubber horse stall mat. Put one in my side x side bed years ago and it works perfect. You do need to allow some air under it, so I bought some left over mesh made from plastic that is used when pouring concrete to keep it from seperating when it cracks. About a 1 1/2" mesh, about 3/32 thick and extremely tough. Laid a piece in the bed then layer the rubber stall mat. That was about 5 years back and no corrosion as water cannot get trapped under it. Just some food for thought here......