It is a well known fact that phone/data signals can be easily interrupted in localised situations. Sometimes even just moving a metre can significantly change the available signal strength. But it is also the case that some of the best caravan sites are not served well by any of the network providers, and unfortunately it may be just the pitch you have set up on that might suffer the poor signal quality. Until there is some way of having all pitches measured for signal strength and made available for prospective users, you are in the lap of the gods.
If guaranteed network access in all places is essential, then your needs may cost more than simply relying on the normal terrestrial bound systems, and at present the only system that can offer such access is Starlink, becasue it is satellite based, and as long as you have an uninterrupted view of the sky, you have a much greater chance of receiving a usable signal.
As for the cost, only you can decide if its worth it or not, but if you need such a service guaranteed then you have to consider Starlink.
Why (edit) not consider cancelling your home terrestrial internet and moving over to Starlink, and simply bring the hub with you on holiday?