For the occasional family local trips in the TJ, I've used the seat belt system on my '98 TJ for my 4yo and a 8mo old with no issues. I recommend having the baby carrier behind the passenger seat due to the seat being able to fold forward more vs. driver's seat. .(Doesn't matter though if you go topless )
I do get a few looks seeing a stroller strapped across the rear roll bars behind a 33" spare but the kids love going topless/doorless.