Introduction and a carseat question

Hi all,

I've been a bump user for years (thebump for 7, but joined theknot 13 years go) but this is my first post to this board. I usually hang out on my birth month club but I had a question so I figured I'd introduce myself here and and ask it. This seemed like the best board because I think folks with school aged children might be most likely to already have 3 kids and know about family cars.

We are currently expecting child #3, and have two others, aged 6 and 3. We've always bought narrow carseats so that we'd have a good shot at fitting 3 across in case we wanted a third child. Amazingly, I think I got them all fit in my toyota corolla! (Chicco Keyfit 30, clek foonf, and diono radian)

That said, we are still going to get a new car soon since we need two anyway, and I would welcome any and all suggestions for a station wagon-type vehicle that would fit 3 across. (We don't want an SUV or minivan--we like to fit in reasonably sized parking spots and absolutely need fuel efficiency. So far the prius V is on the list.)

Here's my immediate question -- when I got all 3 seats across, the way to do it was to install both side seats (foonf and chicco bases) slightly on the side hump that most cars have. They are in there very tightly and solidly, but the foonf especially looks tilted. It doesn't budge, though. I tried searching the carseatlady blog and couldn't find a post on this so I was wondering if anyone else had a suggestion of a place to go to ensure safety.

My second question -- we have an expired chicco keyfit 30 from when my oldest was a baby. We bought a new one for the new baby so as not to use an expired seat. But can we use an expired base in our as-of-yet-hypothetical 2nd vehicle? (I know these are easy to come by and there's always the base-less installation but I was curious about whether anyone had thoughts on this.)