I've got a trek teck window mount, it's pretty good. It's one that has magnetic bases to hold the optic to the mount. Allows for really quick change overs optics to cameras. Got it off the bay for silly money.
Trek-Teach* don't make those anymore. And looking further into my needs it looks like it will be far cheaper to buy a decent 3way head, with QR and fit a clamp. Or a tripod with a 3way on it. The Benbo has served me well but is heavy and cumbersome.