There's a range of things that could go wrong with a rigid connection between the brackets. Thermal expansion/contraction, flex in the camper's frame, flex in the connecting parts, etc., etc., etc.
I'm not to inclined to worry about it, the whole of the system is flexible enough that some considerable distortion, enough so that you've probably got other problems by that point, would need to happen before it would be a concern.
That said, it is easy enough to fix one end of the strut(s) rigidly to a jack bracket and allow the other end to have some float. The floating end could be simply that there is a spacer such that, it the case of 80/20 extrusions, the bolt into the t-nut can't completely clamp the extrusion when run down tight. That would allow the extrusion to slide on the t-nut at one end only.