I have a Minn Kota Ulterra trolling motor on my skeeter Bass Boat.
Because it hangs off the bow so far I have it mounted on a slideing
plate so I can push it back so it does not hit the bow roller when
the boat starts off the trailer. My question is this; has anyone added
anything to the trailer that will keep the boat from dropping down
when coming off the trailer?

I've never owned a boat that dropped down when coming off the trailer, they just float straight back so I've never had problems with Terrovas or Ulterras ever needing to have a slide plate. I haven't heard of anyone modifying the trailer in any way yet. Maybe a different sized bow roller?

Sounds like there a big air gap between the trailer frame to drop down, add a cross member and a roller up near the bow a 1/4 to a 1/3 of the way back

on a real steep ramp the back of the boat floats up an causes the front of the bow down on the roller if you have 2 people to unload the boat when you get back far enough in the water put it in reverse an give it some power off an the bunk boards in the front wont let it drop down enough to hit the bow roller.

This will solve your problem without mods to the trailer.

LiftSaver Trolling Motor Mounting Bracket - Patent Pending
www.liftsavertmmount.com
http://texasfishingforum.com/forums/ubbthreads.php/topics/12060753#Post12060753
http://texasfishingforum.com/forums/ubbthreads.php/topics/12042824#Post12042824

It also saves damage to the TM at docks. If interested contact Ron (Blue Nitro on TFF) or David at Shut-Up-And-Fish.

I have a sliding plate that works fine. My problem is that I want to be able to launch the boat with the trolling motor in the full forward operating position. That would allow me to deploy the TM remotely when launching by myself..