Sorry, HWH = High-Weight Harness. It's shorthand for carseats with weight limits over 40lbs.
Here are some pics I've taken of my Golf - you can judge for yourself if the leg room is similar.
This is the amount of legroom left with a Husky (Regent) installed behind the driver's seat, with the driver's seat all the way back and only reclined a couple of clicks:
(That's about 5 inches.)
Here's the Radian in the same position:
(This is about 8 inches.)
These two carseats give the most legroom because they aren't up on a base like the Marathon. The SafeGuard and Nautilus are both up higher.
Another consideration would be the Apex; it's not generally a favorite around here because it requires a vehicle headrest behind it, and there are other seats with higher harness slots. But if your vehicle has adequate head support (I'm guessing it does since my Golf does), it might be a consideration for you. It's also very low - doesn't sit up on a base.
I just noticed you've still got the Frontier - I'd thought you had returned it already. I think you should be able to install it in the center of your car with the seat belt and the long-belt-path instructions. The nice thing I've noticed about the newer VWs is that they tend to be pretty easy for installing carseats. :thumbsup: