Hey Kristen!
Sorry I didn't reply to you earlier, I had my phone on silent and just now got your text, but it looks like you got some great advice already!
Yes, it is the Radian that I have, and if it would fit in your car right, I think it would be a good choice because it's narrow enough that I think it should be able to fit fine right next to your keyfit, and as long as you could RF it in the center with no problems, I think it would work great.
In our car, a Toyota Camry, I can't really put much of anything RF behind the driver's seat, because dh needs his seat so far back that car seats get in the way. The radian is quite tall, and I can't put it behind the passenger RF either, even though I don't need as much room as dh, but it fits great RF in the center because it kind of goes inbetween the 2 front seats.
I think I saw a post recently where the new Radian XT was put in more upright than the older radians would allow, I think it has something to do with the new RF boot on it.
Anyway, If it would fit RF in the center in your car, I think it would be a good choice because it's narrow enough that your keyfit should fit next to it. I can pretty much get anything I've tried to fit next to my Radian (including my keyfit), and since it's so narrow, an adult can even sit next to it comfortably. It's also nice because the new model, the XT has headwings, which is good for side impact protection, and sleeping, and the Radian has tall harness slots, so you could keep him harnessed probably long enough to get him to booster age. Hannah is probably going to be about 6 when she outgrows it by height.
If you are coming out here anytime before your baby is due, you can try my Radian out in your car, or you can order it from somewhere like Target and try it out, and return it to the store if it doesnt work out. I don't know if they have the XT or not though, but even if not, the 65 is great, thats what I have.
I think the Marathon would also be a good choice too, it sits more upright than an infant seat. I have the Fisher Price model that was made by Britax, same seat shell and everything, just a different weight limit (It even has a marathon cover on it right now). It would fit even better RF in the center than my Radian would. I even got it upright behind the drivers seat once, and thats all but impossible to fit a RF seat there. It's a great, very comfy seat, I love all the padding and the cute covers, and it's so easy to install, I hear it's even easier when it's an actual Marathon, because they have lock off's too and mine doesn't. Hannah will probably make it to 5 in that seat, maybe longer.
I haven't tried out the Evenflo Triumph Advance or True Fit in my car, but those are also great seats if they would fit.
I think I'd try out the Radian and the Marathon first, I bet one of those would work.
Oh, and as far as your dh saying FF is ok because he'll be over a year, have him watch the video from this site:
http://www.joelsjourney.org/index.html It's a true story that happened to someone's grandson.
I'm all for RFing, as you know already. Abby is only FF now because she is too near the RF weight limit for the seats we have. I'm happy she's at least 2 though, but longer would have been better. I turned Hannah back around to RF at 2, and she did until she was 1 month away from turning 3.