Robert expressed precisely :
Power off a USB adapter put a "Three" network free 200MB per month SIM in.
https://3g.co.uk/three-data-reward-sim
200 MB per month should be plenty to check the Hive etc .
If you actually want to use the wifi when you are there just put £5 top up
on.

That is a good deal, doesn't get any better than completely free, but..

There are much cheaper ways to have more data, than the £5 topup - take
a look on ebay for Three data only sims. They do not begin to be used,
do not expire until you insert them. I used to buy a few and keep them
in the drawer of my caravan.

So use the free sim whilst not in your caravan, then when you know you
need a bulk of data use a bigger, paid for sim.

All depends on what networks you can access at the location.