What individuals decide to do with their own caravans is entirely up to them, if their caravan has lingering smells or wear and tear caused by pets, they will be the ones taking the financial hit if they decide to sell their caravan.
I'm no longer a dog owner but I have no issue with responsible dog owners on sites, if the dogs are walked on leads and kept under control around pitches and any 'residue' is picked up and disposed of properly that's fine, the owners are following the normal rules governing dogs on site.
The majority of responsible dog owners on sites follow the rules, but there are always one or two who decide that the rules don't apply to them.
I've lost count of the times that we've been walking along on sites minding our own business only to be confronted by one or more dogs bounding toward us off their leads.
The owners always reassure us by telling us that their dog or dogs are friendly, as they usually are, but we if we wanted to be jumped up and to have muddy paw prints and dog hairs all over our clothes we'd get our own dog, thanks.
The owners who really annoy me are the ones who tell everyone that they 'pick up' after their dog(s), and they do if they know that somebody is watching them.
When they don't know that they're being watched they either carry on without picking up the mess or they pick up, place the contents into a plastic bag and then either throw the bag into bushes or worse still hang the thing from a convenient branch of a hedge or bush.
I've seen distressed dogs locked for hours inside caravans, earlier this year over a scorching Bank Holiday at a music festival the RSPCA had to be called by organisers to deal with dogs locked inside boiling hot caravans and motorhomes, the respective owners were all asked to leave the festival without refunds, and rightly so.
I'm not a dog hater, I've looked after dogs since boyhood and had several loyal long lived best friends until poor health made the prospect of us having one unfair to the dog, but I have issues with irresponsible owners who simply ignore a few basic rules which make everyone's stay on site a pleasant experience.
The O.P. asked '4 dogs, Is that just silly?'
My answer would be, that's up to you. It's really silly if you ignore the rules but if you are proper responsible dog owners then there shouldn't be a problem.