Here's the world's crudest diagram for the DIY setup that we put together on a covered floating dock:

Outer frame (black) is the building structure (in our case, the frame of the covered dock). Canoe (grey) is upside down, with two compression straps (black ovals) looped around ends and each connected to a pulley (blue circles). Two more pulleys (blue circles at top) are fixed to the frame above (our are strapped, but could easily be bolted to a ceiling joist). Finally, two lengths of 1/4" nylon rope (red lines) are fixed to the same anchor point at the pulleys, go down and through the canoe strap pulleys, up and through the fixed ceiling pulleys, and then down to the wall where they are fixed to wall-mounted rope cleats (blue curves on sides).


Obviously, this setup works best with two people, but even solo, I typically lower one end half way, lower the other end all the way down, then go back to the first end to finish up. This very basic block/tackel system is easy enought o use without too much strength, and it stows away with a very low profile.  

Hope this helps!