Glass and Mirrors - Hanging 60lbs mirror

Hi my first post! I have a heavy mirror that is 42" wide that weighs about 60-70lbs that I want to hang over my couch. On the back of the mirror has 2 metal brackes screwed into the mirror frame that latches to the wall screws. unfortunately, the stud gods were not good to me and where i want the mirror to hang has no studs. its a newly constructed townhouse with 3/8" drywall - i think. the walls are very hollow . do you think i can hang this type of mirror up with these walls? and what type of screws can i use in the drywall?

Use a piece of 1/4" plywood (3" X width of mirror frame). At the correct height, nail the plywood using 1 1/2" nails at 45 degree angle anywhere along the length of the plywood. It is not necessary to hit 2 X 4's. Nail the hangers into the plywood to lineup with the hooks on the mirror frame. The plywood keeps the hangers from pulling through the sheet-rock.