I think 1/2" is too thin. 3/4" is good enough for a spindly trailer.
I think anything will rot, but painted exterior wood will last longer. But it's a trailer, it's going to get used and abused. Wood replacement is to be expected. Buy some plywood, use cheapo zinc plated hardware, expect to cut most of it off when it eventually fails. Lather rinse repeat. That is what I did on my lightly used 4x8 trailer, it went I think 10 years on the first sheet of plywood (the 2x4 PT stake sides are still there, despite using zinc plated hardware).
I think anything will rot, but painted exterior wood will last longer. But it's a trailer, it's going to get used and abused. Wood replacement is to be expected. Buy some plywood, use cheapo zinc plated hardware, expect to cut most of it off when it eventually fails. Lather rinse repeat. That is what I did on my lightly used 4x8 trailer, it went I think 10 years on the first sheet of plywood (the 2x4 PT stake sides are still there, despite using zinc plated hardware).
