The super clamp (or a specialized mount such as the window mount by Kirk) might be more stable than a beanbag. My concern is the variability of safari vehicles: some are high sided; some are open; and some require you to shoot standing, leaning on a pipe frame.
If weight is not an issue, take the clamp. But take the beanbag, too, for the times the clamp won't work.
And the Puffin Pad that Eric mentioned looks interesting…
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