I've been thinking about this a lot lately too. Safety for my family and I is paramount. The problem I see with the stock belts is that, in a slow speed rollover or crash the belts don't lock up, so they wouldn't hold you firmly in place. Still a chance of flopping out the window or something and getting crushed. I was planning on going with jsut a lap belt for the time, but the 4-point harnesses they have look pretty good and don't look like they would take too much time to get in and out of. The other thing I was thinking about was window nets to help keep your arms and head inside in case of a rollover. Just thoughts I have as I keep thinking about this.

4-point harness, everything gets buckled at the same time:


Here is a 3-point retractable that can be locked in place once you hit the dirt, maybe the best of all worlds?