Hi - I don't have access to the Portsmouth electoral roll, but as far as I know, yes, people that live in caravans permanently do count...not sure what sort of time frame you're looking at though...some caravans are on fixed sites for example..and rates etc would be paid...
I have access and credits on Tracesmart if it's in recent years you're looking for.
Margaret
PS this site covers all UK and I guess anyone eligible to vote who has no other address would be on the lectoral roll at a caravan site.
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