A simple way to make a mirror block off plate to mount a universal mirror to is cut two/three triangles the shape of the mirror base on the car, drill holes in the lower piece to put studs on. then glue / epoxy the top piece of plastic to hid the holes and stud backs.

the outer piece would be the same process to mount the mirror. just have it all lined up before you epoxy it. once glued bevel the edges and then paint it whatever look your going for.





this is kind of along the lines of what i was talking about..

Side Mirror Delete (Pictures Galore) - Scion xB Exterior - Scion xB Forum