lock n load and head down the road. 8 hrs is not a big deal unless you have a cheap trailer that does not ride well. Stop midway while you eat and let them rest with hay and water
You will probably stop more than that, to refuel and use the restroom. Those breaks will be breaks for the horses too.
Unloading at rests is a tricky thing. For an 8 hour trip it is probably not worth the risk involved.
Be sure to bring water from home so when you do offer water you have the best chance that they will drink it.
Pack extra hay and water just in case there is some delay or emergency.
And most certainly make sure you have all your necessary paper work with you. Vehicle and horse paper work.
I do not trailer a lot either, and understand your anxiety. I basically do it twice a year, to take my horses to my summer home, and back in the winter. Makes me more comfortable if I have company.....just an extra person to help in case there IS an issue, and I got the US rider policy that makes me feel MUCH better. Always get the trailer and truck checked just before I go-I am slightly paranoid, I guess.
Frank, I think Wyoming's point is that an 8 hour ride is not a big deal in the grand scheme of trucking a horse some where, that the horse will be fine. Not that it is not a big deal in general and that it should not be planned for, etc.