Dog smell in motorhome

We purchased a motorhome last year but before we bought it we asked the dealer whether the previous owners had owned a dog or were smokers and we were assured that the answer to both questions was 'NO'.

We have since noticed a very strong 'doggie' smell in the van and we are trying, so far without success, to get rid of the smell.  We have replaced the carpet in the habitation area, given the rest of the carpets a really good shampoo using various products but the smell is still there.

Can anyone offer any advice as to how we can get rid of the smell?

Many thanks.