Do you leave some fuel in and put a stabilizer in or do you empty it?
Ethanol in fuel is good for about 30 days unless a stabilizer is added. Red "Stabil" is good for about 60 days, marine grade Gray "Stabil" is good for about 6 months. Remember, once the fuel "separates" nothing can make it "good again" so you need to protect it before the damage is done.
Honestly, with the money we have invested in recreational gear, is it worth it to risk damage? It's relatively easy to drain the fuel and use it in either the car or truck.....
When I store my 4 wheelers, boat, lawn mower, etc, I drain all the gas, run them until they are empty then use Seafoam to protect them. It just doesn't seem practical to risk damage when it's so easy to drain the tank and treat it for storage.
You've got an electric pump and a nozzle. Using 5 gallon "red gas cans" to hold what you pump out will make it pretty simple to drain the tank. You may need to determine the location of the fuel pickup so you can "tilt" the trailer to make sure all the fuel drains to the pickup. There's no need to make it any harder than necessary, use the tools available to pump gas out of the tank.
I guess you could drain the tank and fill up at a 100% ethanol free pump. we have them here close to the lake. the sea foam claims it can stabilize gas for up to 2 years stabil claims 1. I usually start my generators and other equipment periodically over the winter as well as take the filling station and cycle the gas through it back into the tank.