If I remember right, you have a 12-hr trailer ride back to Florida. I would recommend NOT UNLOADING Gus during the trip. I think you might encounter problems if you unload him to rest in a strange place. He might get nervous and be hard to handle, he might refuse to re-load....
My suggestion would be to have 2 drivers, in case one gets tired. Having a few short breaks here and there for re-fueling and people potty breaks will help Gus rest in the trailer. Offer him water at every stop, but be sure you can SAFELY do so. Don't open any doors unless you KNOW he isn't going to try to bolt out them, even if he is tied, he might try and even if you have a butt-bar or chain. (I'm not sure what kind of trailer you have... some are easier to deal with than others) If you have an open stock trailer, you might consider hanging a bucket in the trailer before you load Gus, and then just reaching in with a hose to fill it when needed. You also might want to bring 5 or 10 gallons of water from the trainer's place. It will be familiar to him, and he is more likely to drink it.
Make sure he has hay to nibble on. Look into a "slow-feed' hay bag, it does what it says - it slows him down and he wastes less.
Make sure he is tied in a manner where he can get his head down to clear his nasal passages. Or don't tie him at all if you have the right kind of trailer. But if he is tied, you don't want him to have so much slack that he can turn around and get tangled.
I am assuming you will stop to eat? Make one of those stops a LONG stop - maybe an hour or two if you can. That will give Gus plenty of time to rest. If possible, find a quiet place to park. I know parking in the "big rig" areas is usually a lot easier, but they can often be noisy and hot. If you can handle maneuvering your rig in the passenger vehicle parking area, it will be quieter, and often has more areas to park in shade.
If something happens and you do need to unload him, do so in the safest, quietest, most enclosed area possible. Preferably NOT on the side of the road, or in a rest area.
I highly recommend an "insurance" and road-side assistance company called US Rider. They will assist you with anything, while most roadside assistance will leave you high and dry when they find out you are hauling a horse. Cost is $119/yr with a small additional activation fee.
http://www.usrider.org/index2.html It applys to the driver, and is good on ANY vehicle that the driver is in.