It should be mentioned, don't ever add anything to any carseat, especially plush-wise. The seats are tested as is, not with extra padding or with any of the extra car seat accessories that you can buy in stores. Even fluffy jackets should be removed before putting kids in car seats, especially if you find you need to loosen the straps to fit the kid+jacket. Here's why: In a crash, the force of your child's body hitting the back of the seat causes all of the air to come out of any jacket or blanket that may be there. When the air comes out, it's like you're squishing it down, and there is a lot of extra space. The extra space can allow for the straps to readjust themselves, possibly coming off of the shoulders and causing the child to fly out of the belt.
We once drove 5 hours with DS in the car, sitting in his seat almost the entire time. Near the end of the drive he needed to get out of the seat, because his butt was hurting. He was in the car seat (I think it was his cushier one, but I'm not sure anymore) and I was in the passenger's seat. MY butt was aching too, I made DH stop the car at the next stopping point, and I held him. It was bad, really. He didn't want to get back into that seat again! He wouldn't sit on his butt on my lap either.
So my advice would be, don't let your kid sit that long in a car seat without getting out and letting him sit on your lap or move around or something.
We've used the scenera on and off since DS was born (as a back up seat). We used it to take DS home from the hospital in, on normal city trips, and on long, long trips. The only time we've had any problems were on long, long trips, but I'm pretty sure it wasn't related to which seat he was in. Actually, DS uses the scenera for sitting around and reading books in. So I guess that means he likes it, lol! His other seat is a truefit.
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