I want to replace the old wooden side door in my garage with a new uPVC one. All the instructions for this tell you to measure to the brickwork and to remove the old doorframe when fitting. My problem is the garage is a 50+ years old Marley garage (pre-fabricated reinforced concrete panels) and it’s virtually impossible to drill into without either damaging the concrete or finding a reinforcement bar. Although the bottom half of the old door has rotted the actual doorframe is perfectly okay. Do you think it would be okay to just keep the wooden frame and screw the new door into it?