I've reread this thread a bunch of times.
After considering the cost of the wood and screws, the potential and fully expected back and shoulder pain associated with installing that many screw, along with the associated blistering in the web of my hand, plus the weight and space of storing these things when not in use, I came to the conclusion that spending $225 on a pair of two piece, 12" RaceRamp cribs (four sixes) was totally worth it.
I measured my Rhino Ramps, and they sit at about seven inches, so two piece 14" cribs would have been ideal (four sevens), but that's not an option. The two piece twelves seemed to be the best choice for me.
Woody - you're always welcome to borrow mine if their height works better for a particular project. They spend most of their life in my shed!
What is the length of each 2x4 used?
Just so happens we made a giant Jenga game and it's in my garage in a giant bin collecting dust awaiting the next graduation or BBQ. (15" each piece x 54 blocks)
I used 10" and 14" for mine, but believe many folks go bigger.