Her truck has the small doors too! And I think it's a tundra...
Sorry. You'll need to read manuals online before you buy one. I measured the depth of the seat and walked around babies R us measuring car seat bottoms to check things out.
The seats in the access can likely fold out to work with almost any seat. We had this problem in our Tacoma access cab (little back doors), but we're able to fix it by folding the seats down/flat to double their width. It also exposes the latch anchors for easy install.
My parents have an Evenflo. The straps on theirs are more challenging to tighten than a Britax so I wouldn't want to use it daily, but for the price/use it's fine. I'm sure they got it on sale at Costco at some point because they are always shopping there...
Which Britax do you have?
We have the Britax Frontier Clicktight, which converts to a high back booster. We used to have the Marathon and the Roundabout for convertible car seats. The critical thing with car seats for us has been the height limit, so I wouldn't buy the Roundabout again and I would pay more for a model that has a higher max height. The baby is still in the infant seat and we need to get him a convertible soon.