Hello, we are occasional drivers (we don't own, just rent for trips). My daughter is 30 lbs at 18 months. I've been using the Cosco Scenera Nxt but today I noticed because her tummy and rear are so chubby, the crotch strap goes under her butt even when installed in the outermost slot. The thing is, we really need a seat that is lightweight, easily ported around, and easy to install as we often have to lug it (along with my older daughter's) on the train for some time, and sometimes in an airplane. Any suggestions? Note we've considered but ruled out the Grace My Ride. Thank you!