I have also posted this on Oct '12. They suggested I ask y'all.

It's getting about time for me to start looking into a convertible car seat. I want to keep Alice rear facing for as long as possible, so a high RF weight limit is a necessity. Here's the catch: I drive a single cab pickup truck. There is an airbag in the passenger side. Currently in her infant seat, she sits in the middle. There's no issues with her fitting right now. I figure I'm gonna have to have the airbag uninstalled or disabled in the passenger side, and I'll have to stick her over there at some point. A new vehicle is completely out of the question due to finances. Gotta work with what I've got.
So, that long winded bit over, the crux of my post: Any suggestions on what seat to look for? something compact with a high RF limit. Does this even exist?? LOL

After 7 years of no ovulation...
BFP#1 10/24/11 ~ EDD 6/29/12 ~ Natural m/c 11/2/11
BFP#2 2/3/12 ~ Alice born 9/26/12


Re: convertible seats
If you want to find something that will rear face a long time weight limit shouldn't be your determining factor. The vast majority of kids will hit height limits for seats light years before approaching the weight limit, so you definitely want a taller shelled seat.
Your situation is fairly unique, so I would actually recommend posting on car-seat.org. You don't need to create an account to post there, although without an acct it takes time for the post to go through a moderator before being visible. That site is basically staffed by techs from around the country (and several international people as well) so they would be better equipped to answer such a specific question based on your specific vehicle.
Good luck and hope this helps you!
After 7 years of no ovulation...
BFP#1 10/24/11 ~ EDD 6/29/12 ~ Natural m/c 11/2/11
BFP#2 2/3/12 ~ Alice born 9/26/12