I had the same problem, as I launch with a Jeep TJ. The wheels were almost always in the water, when launching or retrieving. I realised the answer was to get the boat to slide off the bunks easier, so I replaced the carpeted ones with plastic covered ones. This eased the launching and retrieval, but I found I needed to keep the plastic lubricated with armour-all as the plastic was not slippery enough by itself. If I had to do it again, I would use strips of teflon instead.
As I did not consider this the answer, I then extended the reach 3 feet using a Fulton hinge like this one
http://www.etrailer.com/Trailer-Coupler/Fulton/FHDPB330301.html
Using it completely eliminated the need to back into the water at all, and I found that I could get the boat off without much effort. The only time I had a problem was at the ramp in Coal Harbour, where I needed to use the armour all to get the boat to slide on and off.
Because I didn't want to get my legs wet before or after fishing, I installed a walkway down one side of the trailer, so that I could easily reach the eye on the boat. I also installed an electric winch, with a long control so I could guide the boat on from the walkway and winch it at the same time. Now, I still have to wear gumboots but I store those in the Jeep and no longer get into the drivers seat dripping wet.
I don't know the size of your boat, but I hope this gives you something to consider.