Is it crazy to travel 16 hours by car ( 8 hr there and 8 hr back, 1 day being there in span of 3 days) with a infant under 6 months?
I'd do it. Done many long drives with my kids. Personally I've found that with my kids they were pretty easy to travel with until around 1 yr old, as the motion put them to sleep and they'd sleep for practically the whole drive. I've found that it gets more difficult as they get a bit older than a year or so and end up awake more.
We just did an 7-8 hr (nighttime) drive a few weeks ago with my 4 month old and only stopped once in the middle for feeding/diaper. Obviously you have to be prepared for stops to take longer than they'd otherwise take, but I think she literally only cried a few times during the drive.
That's my experience but I assume not all kids are that way. As with everything related to kids, YKMV.