Hammocks can work.
There are others here that inspired me to do it.
I have a friend with a full size van who installed anchors inside to hang his. Quick and simple, once the anchors/mounts were up. He drilled and bolted them to the supports for the roof (B-pillar and Rear Door Pillar).
Plenty of length in a full size or Sprinter for a hammock.
On a minivan, like my Honda Odyssey, you'll need a properly sized hammock. Hammocks work best with a good amount of sag. 10' hammock or a tad shorter, depending on your minivan. There is no need for a ridgeline, the van roof is your ridgeline. Maybe a custom sized hammock will be needed, to provide proper sag and ground clearance. My 10' hammock hangs with 4-5" of clearance off the floor.
What I do is similar to what the previous videos show. A strap across the roof passes into the drivers side rear hatch. The front side of the strap goes into the front passenger door. If you eliminate all the extra cordage at the end of the hammock it works best, IMO. I larksheaded the webbing loops, (so some custom sewing is necessary to get a proper fit) directly to the hammock ends, shut the doors and your done. Or leave them open for good ventilation.
Structurally, the strap is near the main supports of the van. I'm a big guy and there is no damaging sounds from the van as I enter the hammock. Since the strap transfers the load across the entire roof, I feel it is a safe option. I don't have sunroof, so that may be something for you consider, if so equipped.
Downsides- And these may be deal breakers for some..
Gaskets take a beating. After a few hangs, your gaskets will show some wear from being compressed by your body weight. You may end up with air whistling in at highway speeds. So far, all I can see is a worn spot, and once the strap is removed, no leaks.
Wicking- Rainwater will follow the straps into the van and drip down your hammock. Because of this, fair weather hanging is all I care to do in the van. I am brainstorming a solution to prevent the wicking issue. :-/
I am presently using polyester webbing, 2" wide, aka seatbelt webbing, which is supposed to be the least absorbent of all strap material. Amsteel and muletape (for those familiar with hammock nerd lingo) haven't worked. Its width was chosen to try to prevent damaging the door seals. I did sew the strap to fit my van exactly as needed.
As was mentioned earlier, a hammock may alter your interior lay out, as cabinetry may be an issue. But it is a lightweight (MPG's matter) solution. The hammock can also be used in the trees as normal. It stows away easily and opens up the floor space. No mattress meant more space and less weight. Cost for my DIY hammock and strap was around $25.00.
Keeping warm in the hammock is easier, since you are inside the van and wind is not an problem. A light Underquilt (nerd lingo again..) can work well. I'm using a poncho liner here.
