'Dirt cheap' and 'million bucks' both seem to miss the mark. I'd take an average.
"The devil is in the details."
The trailer appears to be about 8ft long. The tandem axle looks like it needs some rear overhang.
What's the height of the pivot point? Draw a line at 10° from the rear tire, and raise the trailer to clear. Any conflicts?
I'd make an intermediate [hemispherical?] body that swivels on the van floor and has pivots higher up for the trailer. Unless your taking it rock crawling you could ignore the roll axis and let the suspension take that up.
What's the purpose of the windshield and mirrors facing backward on the rear of the trailer? That works against the aerodynamics.
Something like this might work. It doesn't increase the frontal area.
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In the Vimeo video you have a heavy duty flatbed trailer supporting what should be a very stiff monocoque shell. Just put the wheels on that.
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Please don't think I'm bashing this. I admire your enthusiasm. And the Previa. Too bad Toyota didn't make it with AWD
and the turbo
and the five speed. That would be sweet. Canada got the optional tachometer, right?