Equinox/Covertible Car Seat Help!

To anybody out there who drives a Chevy Equinox AND uses a convertible car seat- I drive a 2010 Equinox and I just bought the Safety 1st Go and Grow Sprint and I HATE it. I cannot get this thing tight enough in the center of my back seat. My husband can't even get this thing tight enough. I have to use the seatbelt because it doesn't have LATCH in the center and I don't want him on the sides because thats the only way I can fit 2 boosters in the back too. So to any of y'all out there with an Equinox and a car seat in the center, which car seat do you have and do you recommend it? Thanks in advance!

( I will be posting in different groups to reach more people )