jezza2011 has some great advice. Flooding the engine with fuel oil mix will help protect many engine components. The full throttle, no ignition is a great idea. This configures the oil injection system to mix 50:1 instead of 100:1 as used for idle. If you don't have oil injection it will still work. You just get what ever you mixed as a protective coating.
WD40 is great for displacing water and preventing corrosion. I have also used Boeshield T-9 for the same purposes. It is a bit more expensive, however, I have found that it provides a much more tenacious coating on all surfaces.
Regarding your trailer, you need to also do regular maintenance on the hub bearings. If you don't learn to work on them at home you will learn someday on the side of the road. I would recommend you install some super lube hubs from tie down engineering. Zerk fitting on the back of the hubs allow you to lubricate the back and front bearings by pushing out the old grease while supplying new grease. Not only will it push out old grease it will also push out water or any other contaimination that may have intruded. If you anything other than grease coming out it is a good warning sign that you need to replace the hub grease seals.