Obvious question but what size cover should i get for my Work n Play?

[Walks]

I know it seems like a very obvious question.

Its a 17 foot so I'm assuming i need a 16-18 caravan cover. Is this correct?

Something like this? http://www.ebay.com.au/itm/Heavy-Du...Caravan_Parts_Accessories&hash=item3f1e2cd75e

 

[Grano n play]

I bought mine from jayco caravanland , and they advised to go a little bigger , so I went for 18 to 20 size. I havnt used it yet , will use it more in summer. Also lucky I havnt used it yet cos I found I had a leak coming through hot water system latch, will get fixed under warranty next week, by the way I have w n p also , 3 months old.