Keeping the Vents in???

How in Thee Hell (my dad always says that), do you keep the vents in? My 68 coupe that had factory A/C, is a royal pain in the butt trying to jam those things up and get the hoses connected and getting the little plastic "clip" into the little hole while trying to make that spring clip attach to SOMETHING!! What's the secret? Or did that question even make sense? Both sides, same thing.

No help? Nobody?