My theory on floating... The float isn't home, and I don't want my horse to think it is. It is a modeof transport. I want my horse to learn that they go in, we go somewhere, and they get to get out. I never load and unload my horse without going somewhere. Even if we have to use a butt rope, or it takes a while to load, I never unload and do it again. That isn't a reward. They get on the trailer, what you wanted, and instead of going where you're headed and getting off, they are made to do it again. Just doesn't seem like the best way, in my opinion. The journey and getting off at the end is the reward for getting on. Using this method, every horse I have/had has become a self-loader within a month, and stayed a self-loader for the time I've had them, and the ones i'm still in contact with are still self-loaders.
If your horse has problems standing still while mounting, you get on and off a LOT. If your horse does something goofy in a certain place in an arena, you go by that spot a LOT. If your horse is scared of an object, you introduce them to it a LOT.
My horse is afraid of the trailer. So when we have a trailer session, which isn't often, I admit it, but we spent a LOT of time working on it. We do Clinton Anderson's method by the way, even though I didn't know it at the time. So my horse only deals with the trailer every two or three months, and we don't go anywhere, but we get in and out a lot. I don't want it to be a big deal. I don't want her to finally get in, drive for an hour, and decide it wasn't fun at all, and not get in on the way home.
And she does get a reward. When she gets in, we unload and take a break, let her graze for several minutes, love on her, brush her, and do it again. She knows when she unloads she gets all sorts of good stuff, so she needs to load to get the goodies.
And to take it further, if my horse gets banged up and needs to see a vet, I need to know my horse will load. Sometimes, you don't have all day. Sometimes, you need to get in and go.