I know someone who fit a BIG
Britax (65 pound weight limit one) in a Porsche 911!
You don't need a full 45 degree recline angle for babies who have good head and neck control. That's only necessary for newborns. Install the
convertibles as upright as is comfortable for your baby. Use the
rear-facing tether. Brace the carseats against the front vehicle seat(s). Voila!

__________________
-Jenny
Mama to Hayley Rayanne
5.5 years old, 48 inches & 48 pounds
in a Britax Husky, Britax Parkway
and Compass B510