We tried something new this weekend for baby transport. Normally, we have this baby seat strapped onto the SnapDeck of the Xtracycle (pictured above). It works great, but I don't like keeping it attached to the bike all the time. It's really big and gets in the way of any cargo hauling on top. So I find myself spending a few minutes to take it off and put it on all the time.
Here's what we went with this time. We put the little guy in his old car carrier and strapped that into the trailer. We made the mistake of putting our older kids in the trailer when they were too young. They were safe, but the instability of it made them a lot more apprehensive about riding.
We were able to strap the baby carrier very securely inside with no wobbles, then use it's five point harness to strap him in. He wasn't going to budge. And he seemed to like it just fine. This may be our set-up from here on out. He seemed to think it was comfortable enough and it doesn't take any time to work into place.
Get out there.