I'm thinking about foam again... maybe you could cut strips of foam thick enough that, when jammed into the ends of the PVC pipe, it won't slip out but still provides variable angle flexibility.
You'd have four base corners (3x intersection) and a peak (4x intersection) to join; so the area of the cross-section of the base corner strips would be ~1/3 the inner diameter of the pipe, and the area of the cross-section of the peak strips would be ~1/4 the inner diameter. Make them long enough to stay in, but short enough that the third/fourth one you insert isn't too hard to get all the way into the pipe end amongst the other two/three. Add an extra inch or so for the fold in the foam (as it bends to conform to the given angle) and you should be set. Your PVC pipe will provide static tension, to hold the pyramidal shape, even though the actual joins are flexible to the point of being floppy.
The cloth sewing will be even easier to figure out (but not to do, of course), and I leave devising a pattern that let's you put the PVC in sleeves along each edge as an exercise for the reader (hint: it's about identical to making cardboard patterns, as explained in earlier posts to this thread).
JK Grence wrote:
> Now all I need to do is find a place that has PVC pipe joiner bits in
> that odd angle setup!