I'd do it. You're way under the weight limit, and you have a nice rack that doesn't stick out too far so there shouldn't be any problem. The hitch attaches to the frame with just 2 bolts, but It's not like 142 pounds is going to rip the hitch off the frame on a 20 minute drive to the trail. Crawl under the car and check it every once in a while if you're worried about it. If it doesn't work then you're only out a hundred bucks or so for the hitch vs. whatever it costs these days for a nice roof rack.
If I went to the trouble of getting a roof rack, I'd put all four bikes up there and not mess around with the hitch rack.