Yeah, btw, my "mesh" of Vodafone THG3000 hubs works great, as recommended by PedroC. I got 2 of them, must have spent under £15 in total and they cover our house and garden very well.
These things have beam forming, very good bargain!
I got my mesh of BT Whole Home disks on sale for £100, 4 of them so I have one in the lounge, conservatory, bedroom and office. I can get WiFi at the pub opposite my house!
Thanks all for the ideas and suggestions.
Planning for CAT 6 in the final house build, originally did use cable for TV, but then realised there was a NowTV dongle in use with no ethernet. Mesh seems a bit OTT for a caravan, just disappointing to have such a poor range, but will percevere.