I bought one of these tunnels recently:
http://www.petsathome.com/shop/large-small-pet-activity-tunnel-by-pets-at-play-15846
What i did was feed the ramp through the tunnel and tie it to the bottom and top cage bars so it doesn't move - i suppose you could also attach it to the ramp using velcro (i have seen iron on velcro strips in sainsburys).
I would definitely look in to re covering your ramp using an old piece of carpet. I did see a pic once of someone that covered their ramp using an old gym sock

They just attached it by putting the sock over the ramp and using velcro at the top 'open end' (enabling them to remove it for washing)
There is also a site that makes specially designed ramp tunnels (cant think of the name off hand - will have a search for you)