Some of the private ramps along the river here in Parker are pretty shallow. To get small boat and PWC trailers deep enough, lots of people fab up two-wheel dollies like those used to tow aircraft. One guy actually made his from one of those actual aircraft dollies.
With an extra 10-15 feet of length you should have no problem getting the trailer deep enough to float off/on.
At the top of the ramp with the wheels chocked, remove the dolly, hook up the trailer as normal for highway use.
Here’s an example from Google
View attachment 8763