For what it's worth, for 90% of trailers and ramps, when you back the trailer down, don't put the trailer any deeper than the tops of the tires. This may look like it's too far out of the water, but try it. This makes it MUCH easier to load in wind and current. The boat will go up and center itself almost automatically. No butt-end of the boat floating sideways or out of level.
Depending on your HP, you can either push the boat most or all the way up with the motor, or you may have to crank a small HP boat the last foot or two. Even if the latter, it really beats trying again and again to get the boat on straight.
I have helped many, many people with this tip, and very few rigs won't work with this. Guides still can help, but this greatly reduces the need for them.