I've drawn a vehicle spaceframe. I now need to have a 5mm plate sitting on the front surface this triangular arrangement of three tubes.

The lines you see in the tubes are the 3D sketch used to create the tube members.

The only way I could think of drawing the plate is to create a new plane using the 3D sketch lines and then offset the plane the same amount as the radius of the tubes, so that the plane sits on the tubes. Is this the cleanest method though?