If the Chase is new, I would try to return it... you won't need it.
The Triumph Advance is a really good option. It will allow your little guy to rear face to 30lbs and then he can go forward facing in it until 47lbs. The top harness position is actually just a touch higher than the Chase, so it will last until your son is ready for a booster seat (approximately 5 - 6 years old).
The current recommendation is to rear face to the limits of the seat. I like to encourage parents to go to at least 2 years old if possible. There is a ton of information on this site about rear facing, you can use the search function or just ask and people will be glad to pass on a ton of links as to why it's the safest choice.
Since the Triumph sits up on a base, it will leave hip room for people to sit on either side of it. It may be slightly tight, but I think you'll be okay.
We had a regular Triumph and used to put it in the back of a Cavalier with two adults on either side. It was a little squishy, but it worked fine. The sides of the Triumph made nice armrests when travelling.
The most important thing is to make sure you are looking for the Triumph *ADVANCE*. It will have red tabs up by the shoulders (infinite harness adjustment) and red knobs on the side, instead of the yellow knobs that are found on the regular Triumph.
The Advance is showing up in Walmarts for $144 (brown colour) and can also be found at Sears (black colour) for the same price.