We have had both Fiamma 45 and 65 , one fits flat on the side, and the 65 fits on the roof of lowline models.
We now have an Omnistore which is fitted recessed into our Autotrail, we use it mainly as a 'Rain cover', to keep us dry while I feed the dogs, and clean them up after a walk. Wouldn't be without one. ALWAYS use secure Straps held with strong Pegs. In case a sudden wind blows up.
http://www.toolstation.com/shop/p35959?utm_source=googleshopping&utm_medium=feed&utm_campaign=googleshoppingfeed&mkwid=4RpE9wmZ&pcrid=46335358943&gclid=CjwKEAiAo8emBRCX_OqU4qek6y8SJACz
These are cheap and very strong.
We do take it down if it is windy overnight, as the flapping keeps us awake, otherwise it stays up,Whatever.
ps Always keep it 'Tilted' to allow the rain to Run off, Water is very heavy. Ray