Just finished reading your caldwell fire control review.
As far as breaking down the rest for transport, why not incorporate a clamp, like the ones used for clamping a bicycle seat to the bike frame? One tube is slotted and the other is fitted snugly into it, then the clamp is secured. The result is rigid. If it can hold the weight of a cyclist, it can surely do the job on the rest tube.
Phil, aka tazzman