Any parents here with convertibles? I have an R57 on order, and have 2 boys, 3 and 6. My 3-year old's regular Latch seat with harness did not want to fit in the back seat of the Mini we test drove, and I was uncomfortable with either of my kids just using their booster seats with the built-in 3-point safety belts when we had the top down for a bit (though everything seemed alright). They will only ride in this vehicle on a rare occasion, as we typically travel in my wife's Honda Odyssey if the kids are with us. Still, I have to think about this - and I rather think I'd be more relaxed with 5-point harnesses for them, even if I never put the top down with them in the car. Any suggestions on boosters using the Latch system and having a built-in 5-point harness - or would it be easy enough (and legal) to just install 4 or 5-point harnesses in the rear seats and run it through the belt guides on a regular booster seat?