My comment following Safari
My conclusion regarding beanbag vs Tripod/Wimberley for motor safari lens support, following my Dec 2008 Tanzania trip:
Though I did bring my tripod and Wimberley head, in a safari vehicle, the bean bag was the support system of choice.
1. I could easily change photo positions in the vehicle; no futzing with the setup, just flop the bag where you want it and fire away.
2. The empty beanbag was nearly weightless for air travel.
3. Beans were available at local markets.
4. The beanbag was very durable and adaptable, damped vibrations, and gave secure support for my 500mm.
5. At at the end of the safari, the beans became a delicious addition to our menu!
Just to see if it would work, (I tried it just once!) the tripod/Wimberley head combo in various configurations in the vehicle. All the possibilities were cumbersome, it was difficult to shift positions, and this rigid setup was extremely sensitive to vehicle and personnel movement and vibrations -- inside the vehicle, it was more of a liability than an asset. The beanbag definitely was the winner!
The tripod/Wimberley rig was only useful for short walking safaris and around lodge grounds for birding and scenics (Clients are strictly prohibited by regulation from setting up outside the vehicle while on motor safari). For most tripod applications, I could have saved luggage weight by leaving the heavy Wimberley home, and used my ball head instead.
The exception was on the shores of Lake Eyasi, which were teeming with Pelicans, flamingos, Ibis, storks.... There, on the ground, free of the confines of a vehicle, the Wimberley was clearly the best tool for the job.
Happy travels!
Craig