You should be fine with the carpet. It's the direct contact between the PT wood and aluminum. Some PT woods will do it, some won't. It all depends on what process was used to treat the lumber. You'll know if it happens though. Typical looking corrosion will start to show up. It certainly isn't going to happen overnight. Just keep your eyes on it. I doubt you'll have much of an issue though.
When you coming to build me a trailer, Jared?