First of all, there is no way I would be securing my new G614's under the trailer for a year until I was ready to put them on. $1,400 to $1,800 worth of tires to steal?
I would have them installed. Don't know what the weight of your fiver is, but I would take that into consideration when deciding on exact tire pressure. Also, remember the temperature outside effects your air pressure reading. In other words, if it is 40 degrees when they go on and you have them inflated to 110psi, don't be shocked that in the spring when it hits 75 degrees that they read 115psi. I keep mine slightly below 100 currently.
I don't use covers on my tires. The main reason I don't is because of my slide configuration. My tires are all in the shade 90% of the time. If I needed to cover them I would never use plastic or vinyl covers because they are a scam and will hold moisture and actually cause your tires to rot quicker than UV damage. If you want to protect your tires from UV, keep them clean and coated with 303 like has already been mentioned, and if you do cover them use a high quality screen type cover.