We haven't installed ours yet, so we can't be sure this will work the way we intend, but our thought was if you keep the weight of what you are lifting down, using a light-weight frame and slats (we use Ikea slats), and a foam mattress, no plywood, the whole thing is light enough we plan to lift it with small pulleys on the 4 corners attached to the ceiling and rope. We will have nylon cleats to tie off the rope - marine hardware - on the bed supports below.
Once it is up, we will have some sort of a swiveling wooden cleat to keep it from swinging back and forth when we are driving. We have determined that the bed will clear the reading lights when we hoist it. We would have one person at each end with 2 lines each, so the height and clearances can be watched.
You might wonder if it so simple why we haven't done it yet... we have had our van since 2009?
The answer is that so far, we haven't run into the multi-day bad weather stretch that would make us feel like we wanted to sit in the van, rather than outside. Plus, we have enough stuff stored under the bed when camping that we would have to move outside, we just have been too lazy to do it. But we have the hardware and line and will probably get around to it at some point. I need to find ways to put everything under the bed neatly in storage containers that will slide under the van when the sitting area under the bed is needed.