There are some very nice trunk mount racks out there but you always run the risk of scratching the paint where ever the rack contacts the car. Even the ones with really nice feet on them. Also I never felt they were as secure as any of the other options.
That said I have never had an issue using one either. I really like the saris bones rack if you wanted to just get a trunk rack to get by for a bit.
Saris Bones Rack - $130 range. Super adjustable and pretty sturdy. You can definitely clear a small spoiler with it and adjust it from trunk to hatchback to SUV.