Can I safely carry it in my car
I'd recommend you put it in your trunk, if you've got room. Today's vehicles are incredibly crashworthy, but imagine being in a rollover with a fifty pound hunk of lead bouncing around inside.
I think a Group 24 is about the smallest marine battery they make. I think they've got about 40 useable amps, so a Fantastic Fan would run for fifteen or twenty hours before you'd begin to damage it.
Tony