In this post I'm going to try and explain my steps to installing a hinge assisted bed/couch in a 2004 Toyota Prius which also includes enough storage space to haul your gear. First off find an awesome family which has a useful (although a little unorganized) shop space or own your own shop with tools and stuff. Then you take a ton of measurements of the back of your Prius because nobody on the forums can give you a direct answer - until now.
The above graphic (click on the pic for larger view) shows the measurements (rounded off) for the trunk/rear seat width and length. There is 38 inches of available space on the bottom of the trunk, 40.5 inches in the upper wheel well area(although, I was able to go to 41 inch slats and just stretched the fabric), and the available space from door to door is 51(I cut the slats to 48 inches instead because it is easier to reach our under-bed storage compartments). And finally the realistic length from where the door shuts to the seats in forward upright position is 73 inches. Also the height from trunk floor to ceiling varies from ~18" to ~36".
The next step, was to remove the rear seatbacks which ended up being just the removal of four 14mm bolts attached on top of the folded seats under the velcro cloth. They pulled right out. Then, I was able to remove the actual rear seats by folding forward until they click then laying them flat again and lifting straight up. The only drawback I've noticed from this is that the sound of the hybrid engine engaging is actually noticeable now.
Then get your tools out and ready to do some work. I used a 1/2" winged bit, table saw, miter saw, screw gun, nail gun, and a belt sander to do the job. Along with various measuring devices. I would imagine if you had the wood cut the right width you could do it with a handsaw, hammer, and a 1/2 drill bit, and screw gun.
I then cut a 2x6 into two 2x3's for the runners of the frame which I cut at 68 inches. I also cut the legs for the trunk and rear foot space - the trunk legs being ~7 inches high* and the rear foot space legs being 20.75 inches with a .5" foot. I then attached the trunk legs with two 3 1/2" screws and the r/foot legs with one 3 1/2" screw in order to turn the 2x4 outwards so the hinge could rest there.
*I kept the space between the trunk and the bottom of the bedframe just under 7 inches high so we could slide our storage bins in and out.
The next step was to cut the slats to the right lengths. I cut three to 40 inches, two to 41 inches, five to 48 inches, and a final 48x6 inch headboard. I attached them via nail gun (way quicker then screws) to the runners, two inches apart with the first board overhanging one inch towards the rear of the trunk. The last two boards toward the front of the car were attached to a 1x4" board which rotates on 3/8 x 3 1/2" lag bolts. The 1x6 is 17 inches long and attached 15 inches from the end of the runners for a two inch overlap. This allows for 72 inches of total bed length which is exactly my height and it seems comfy so far.
The secondary runner on the end of the bed allows us to fold it up into a lounging position for reading and just hanging out. It also allows us to have a full-length bed but still be able to put the seats into a comfortable driving position without moving the bed around. As you can see in the above photo taking out the seats allowed for a lot more under bed storage freeing up space for our bike wheels and on the other side, a shelf for odds and ends. If you have any more questions about the measurements you can email me at tigerinourcar@gmail.com.
