My valences appeared to be screwed at the top into underside of the cabinets. I removed the side screws and bottom screws and they would not come off. So not having a way to put those screws back in place, I left the valences in place and installed the MCD shades in place. It is easy enough with the spacer that I don't see a need to remove them. I used a long Phillips bit too, but not 12". I would love to have had square drive screws!! I got them to clip in by feel like ernieh said, not by sight.
I made a simple cardboard drilling template that made drilling screw holes easy. If I did it again I would use a wood block as a template.
Somebody asked if the MCD shades are that heavy so as to need support. Definitely not.
A table knife works well to unclip them if you ever need to remove them. It is thin enough to fit between the roller and the valence.
'04 Alpine Coach 36' MDDS