You have a couple of problems there. Apart from poor signal on Vodafone there will also be capacity issues when all the holiday makers, mobile home residents arrive. Many mobile home people use routers for mobile broadband and, if concentrated that puts a big strain on the network.
As a Virtual Network there is nothing Virgin can do about signal. That's down, in this case to Vodafone
I can only say that this year Virgin will be making the final move to O2 as Virgin Media and O2 combine.
My advice would be to get a PAYG test SIM (Giff Gaff or Tesco) which use the O2 network and check things out.
If the signal proves unsuitable then you really have no option but to move to the best network for your location.
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