Awning Advice

Hi All,

I am new to caravanning so please be gentle :-)

We purchased a caravan last year and have been out a couple of times this year. The caravan came with a porch air awning which is great, however, I am looking for a larger awning with an annex. 

My question is around sizing. The rail on my caravan is noted as being 1010cm which I believe is a size 15. Can I purchase an awning that is a size 12, would that still work or would it have to be a full size 15? I am looking at second hand awnings to start with so trying to find if I can by slightly smaller than the full size or if it would have to be the full size to work correctly.

Hope that makes sense

Many Thanks

Sean