I wouldn't buy one without a power tongue jack. the vent covers are a necessity, as you can leave the vent itself open a bit and not worry about rain getting in.. also it will protect the vent itself from hail during summer thunderstorms.
If you are going to be leaving trailer sitting without being plugged in, you need to find a way to disconnect the battery.. the co and propane leak detectors will drain your battery in a week or two.
One really cheap mod I saw was a hook mounted near the outside shower to hang the head on during the time you are there and using.. learn to use that for cleanup, it will help keep the dirt, blood, etc out of your new trailer.