I chose 16g steel tubing, and welded three separate bed panels then screwed on 1/2" ply, and later glued carpet on top.
WhhiteWhhale, thanks for the example. What was the dimension of 16g cross members? The photos look like 1"x2" with the 2" dimension vertically oriented. Do you get much deflection when you're seated on a single panel (a common scenario when you're climbing onto the bed)?
I bought the aluminum side rails( your choice of height) and built my own frame out of .083 1"X1" square tube. I put a 5/8" ply on top and have yet to do the mattress - I am liking this Froli product mentioned above.
Ticktok, same question to you: how much deflection are you getting when seated on a single panel? The online deflection calculators show pretty extreme deflection for 1x1 .083 steel. With a 65" span using 1x1 .083 and a 100 pound load, the deflection computes to
7.09 inches! With a 200 pound person potentially applying their entire weight to a single panel (an unavoidable scenario when you enter the bed, it seems) the 100 pound load doesn't seem unreasonable. In fact, if you consider someone sitting on the edge of the first panel (again, a reasonable scenario) then the load on the edge tube would likely be > 100 lbs. even when considering the distribution of force via the panel cross members, plywood, etc.
Obviously having some center support is an easy way to reduce deflection, but for my uses I place very high value on a completely unobstructed compartment below the bed. So I won't compromise on the "full span" platform, but I am willing to utilize whatever materials/design is necessary to provide a robust solution.
I'm having a hard time believing the online calculators, but I've tried several, and they are consistent. For example, a 2 inch diameter .083 wall steel tube across a 65" span deflects nearly 3 inches under a 200 pound load? That is much higher than I intuitively expected. I guess that is analogous to hanging by one hand from the center of the span; perhaps I should find more sophisticated calculators using a load that is distributed wider (ie, butt cheek width, or knee width when crawling on, etc).
Once your weight is distributed across the platforms, the load on any given beam is relatively negligible, so the "sleeping scenario" is easy to design for. But I think that much more severe scenarios are unavoidable. Imagine, for instance, two people sitting together on the edge panel! So part of my solution will likely involve a larger and/or thicker tube at the very edge (van center).