"Ahaa, that's alright, I've got a good grip..." And there was virtually no room at all in the cockpit, let alone good viewable to watch for things coming there way, so Vash choose to risk life and limb rather than... risking life and back pain.
He listened to the explain with a straight face, but at the end of it, there was a slightly comical panicking 'oh-geez-what-did-we-get-into' look to the expression. "... Ran over a few cars? We don't want to run over any cars, do we?" Well, he figured Len wanted to roll over some tanks, but, really- did they have to go that far?
Now he was wondering if any of that pacifist talk (mainly consisting of the lovely motto 'love and peace') got through to the other. Ah, well, they'd... see.