Bike racks

I'm shopping for a trunk-mount bicycle carrier for Daughter's car.
It's a 2009 Pontiac coupe and it has a little spoiler on the rear
deck. (not sure if the spoiler is a problem or not) Any
recommendations for a good rack that will hold 2 mountain bikes or
cruisers, won't scratch all the paint off the car, and will allow
the trunk to be opened (carefully) with the rack still installed and
bikes removed?

I've been looking online at the Thule models 910 and 961XT. And
maybe a Saris Bones II, but I'm not sure I trust that one because
it's all plastic.

Thanks,
Bob