why are they doing that on the frame?
Different strokes for different folks I guess. I can only speak for me and my process but the first thing I do, before ever picking up a piece of sandpaper, is remove the body. After that it gets sanded, the parting lines ground, wheelwells and cockpit trimmed and then the filler goes on to shape the parting lines, etc. Once that is done I cover the interior and engine compartment with plastic before the body goes back on so that the doors, hood and trunklid can be installed and then the bodywork to trim, fit, shape and gap them is performed (this has to be done on the chassis to get proper fit and contours). Following that the body comes off again to begin the process of high build polyester primer, 2K urethane primer, sealer, base and clear with the appropriate sanding done between all. Doing it this way prevents the interior, engine compartment and chassis from getting covered in dust...and believe me, there is A LOT of dust!It's their process. From what I can tell they fit the panels and shape the flares before removing the body for the rest.