Wendy I have tried various ramp covers and tried to invent some that
covered that area and what I have found works best for me and the
ferrets are some long mens work tube socks, I get them at the dollar
store. They are tight and come up well above the end of the ramp making
room for it to fold over on the top, when the ramp is attached its very
solid and no gap remains. I top that with a shelf cover with corner
slots to hold it on, that way it comes over the edge and covers the
top of the ramp area. So far with 6 ferrets in a ferret nation for
over a year we havent had any problems.
Pics of underside of ramp 
http://i65.photobucket.com/albums/h219/mysticalmanana/apr30-08003.jpg

Pics of top side of ramp
http://i65.photobucket.com/albums/h219/mysticalmanana/apr30-08004.jpg

I hope this helps

[Posted in FML 5958]