I've got two -- the black one and the silver one.
On the black one, I gutted the interior, put in a cockpit from a Snowcat so it could fit two people, then screwed around with the innards until I was able to make the "transformation" effect work while still fitting two people inside. It was a pain in the ass, but it works pretty well. I should have done a tutorial for it, but I'm never trying that $#!@ again, so.....
The silver one I use for Matt Trakker - I haven't modded anything yet, other than fixing the sunroof so that it doesn't pop open unless I want it to. Trakker is WAY to tall to fit in the thing, so I just leave him out of it. But since there are no windows anyway, it's not like cramming him into the thing adds to my play value (which is why I disabled the sunroof.)
Smaller Joes will fit in there just fine - but remember that when you transform the thing, the seat slides back (the Bruce-to-Batman feature). I would still recommend picking one up - just because it's fun transforming the thing back and forth
