OK, I didn't QUITE think straight on this one. Right track, wrong wheel base.
OK the REAL way to make foam work would be to get foam thick enough to jam firmly into the PVC end, when cut into a 4-way cross (an X) or 3-way cross (the shape inside the circle of a Mercedes logo). So if you're using 1/2" inner diameter (ID) pipe, then you'd want ~3/8" thick foam, and the cross-members would be cut ~3.8" wide. Use the 4-way for the peak and the 3-ways for the base corners. Leave a large enough "center square/triangle" in the cross to allow for flexing to the acute angles necessary to join all the pipes together. Again, static tension will keep them together.
Sorry if I got confusing with the whole "strips" notion below.
From: David Artman <david@xxxxxxxxxxxxxxx>
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.