Build yourself a transport box for the model, slide up side, or lid version, all of my current up 'todate' projects now get stored and transported in solid ply boxes, they fit in cars easier, there is no damage in transporting them, and you can stack them in a location easily,some boxes are fitted with pre cut carry handles others have rope handles.
A 'bag' will never offer you the protection you really want for your creations, a box is the best way i've found to keep those models in top condition during the rough handling.