...The vertical pillars are enough to support a loft bed E-track without problem.
A quick and easy method would be to bridge the higher space with a length of 1 x 6 dimensional lumber. I would use 3 each fasteners with fender washers to attach the board at the places where the body metal is available. (That should yield 6 each body fasteners per side. The dimensional lumber can cantilever out a bit if needed.) The E-track can then be attached to the 1 x 6 by pre-drilling and using sheet metal screws....
vic
Thanks for helping me with the perfect solution for my build!
As this is a full-time, all-weather, build I'm already using 1x3 as vertical furring strips to frame it all out with a good layer of insulation. I was stumbling over how to best attach a good sturdy bed frame at about 38" high while trying to maintain a bit of a thermal break and work around that shell. I'm going to do what you suggested but I think I'll just lay out the horizontal 1x6 across the whole length of the van to keep nice even lines the whole way. I'm not sure I would have felt good about using 1x6 across the gaps for a bed support with most other setups I've seen, but I imagine steel E-track bolted into it makes for a very sturdy combo.
For the whole length of the van the horizontal 1x6 will be a good anchoring point for wall panels. In the back the 1x6 will be the perfect spot to mount E-track for my bed, And in the front of the van it will be a good height to secure cabinets and counter tops.
For the bed I'll probably do a heavily-vented sheet of 1/2" ply fastened down at a handful of points with wood screws.
I'm going to take a look at some of the hardware at the store tomorrow but I'm thinking if the brackets are deep enough I might only bolt in the 2x crossbeams on one side. Maybe alternate so one crossbeam is fastened on the driver side, the next one on the passenger side,.. I imagine that would allow for a bit of flex in the system which I've heard is a good idea. Am I nuts to attempt this on a build that regularly goes down terrible forest roads?