I just recently moved into a house with a side entry garage pretty far back from the road and significantly elevated at the garage. The driveway has a pretty good slope, so was beyond concerned about overall safety and potential of losing control of the boat when attempting to get into the garage. To echo a comment above, if I try to back all the way in, I too would drop the truck off the retaining wall trying to make that 90 deg turn into the garage.
I looked at all the available options for a tow dolly and decided none were really going to meet my need reliably (meaning if I lost control of the dolly, the boat would then go over the retaining wall!). My final solution was actually the most effective and lowest cost. I purchased a
120 V electric winch from Harbor Freight and mounted at the rear of the garage in the concrete floor with Redhead anchors.
I then back the boat up the driveway and just park it at a 45 deg angle in front of the garage door. Put wheel chocks in place, and attach the winch cable to the trailer (using 2 tow straps slipped over a cross member on the frame), disconnect from the truck, then have my wife push the button to winch on into the garage.
I have bit of a slope (thus my concern for the powered trailer dollies), but the winch doesn't even bog down a bit. I use an inexpensive
hand trailer dolly (also from Harbor Freight) to guide the bow in as my wife is winching it in. To get the boat out, we just do everything in reverse. Doesn't take long now that we have a pretty good routine worked out.
Two potential problems though... 1. This solution requires two people... one on the winch control and the other on the bow with the trailer dolly, and 2. You REALLY need some slope or getting it back out of the garage would be tiresome. When in the garage it is on a flat surface, but move it about 2' when winching it out and the driveway slope just takes it right out on it's own.. no pulling or pushing. I would hate to have to manhandle it if on a totally flat driveway.