Don't rely upon a single beam or spot to support a hammock, especially for two. Distribute those points of weight carrying with a piece of strong hardwood or metal wider than a single point.
As a decades long hammock man, I have always had a hammock in my vans over the years.
For my 06 2500, 158", I mounted the rear hook support at the point of the opening in the bulkhead over the rear axle. I have cut a 3' square window of sorts in this bulkhead so I can crawl back there without having to go outside. I do have a futon bed I can put into the rear storage area on top of some floor cabinet storage pieces I put in.
For the front, my van came with a shelf above the driver and front passenger seat that the original up-fitter provided. Just above the windshield in the center is a 4" by 6" panel that I removed and installed a piece of hardwood at least a foot long by 4" high into that space. To this piece I put a hook before replacing the decorative panel back into place. The headliner is able to support my hammock. The might not be the case for two people. The seats that came with my limo set up can be moved out of the way with the steel floor mounted brackets, to give the hammock the space it needs.
A hammock for two is a blast. With the ford and chevy vans I had decades go, a simple metal hook with four steel screws into the framework was sufficient and never pulled out. For our Sprinters, there is a lack of strength that needs the weight distributed across a couple of beams, if not more. Maybe a piece of iron across several beams could handle the weight of two. The front above the windshield is problematical. The beam above the front seat may be the only point that could used support. I needed the extra length above the windshield mounting point I chose because of the bulkhead above the rear axle. You have to work with what you have.
I did come up with a portable hammock stand that comes apart in pieces for easy storage for setting up under a tarp off the side door. Those outside yard rope hammocks are brutally uncomfortable, but the steel stands that come with them can be made to work with the string hammocks by adding some pipe pieces to elevate the hooks on each end in a curve back bending of sorts. The top pieces need to curve so the hammock clears the hammock stand support ends. Sorry no pics from this dinosaur.
A thought about using the hammock points of support in our Sprinters. Having a temporary vertical to the floor piece of pipe or wood at the hook points, could prevent sagging of the beams, and be an easy thing to remove when not using the hammock. The Sprinters beams need some reinforcing, thus my first thought about distributing the weight. Its all food for thought and there many ways to achieve what you want. This is just one or two. Thanks to all here.
