Oscarvan,
I am in the process of building a 12 ft toterhome with two slides 41"X 78". I purchased the floor and wall assy's from Liftco inc. They sell numerous types of slide assy's in any size you may want. I have yet to install them so I can not address the amount of difficulty at this time. Mine are the above floor "touchless" (no floor rollers). You may want to check their website. I called several slide-out manufacters. All except Liftco wanted me to have my engineering dept call them or send drawings! I'll post photo's when I begin to install them. Also, you may want look at a little wider slide, 24" is pretty narrow for a couch. Liftco advised me I needed 40" for a sleeper sofa.
MMM