Hiya, its going to depend on what you like, sea or mountains etc.

If you want the coast then its going to be a bit crowded at this time of year especially with seasonal northern European motorhomers but if you don't mind that then there are some great camper parks. Where possible I'd book ahead. Otherwise take pot luck as there are lots of stopovers around these days.

One coastal place I'd recommend is Calpe between Valencia and Alicante, its a place that has a lot that stays open in the winter months. Several places to stay there, this is the one we stayed at earlier this year https://www.clubmotorhome.co.uk/motorhome-stopovers/motorhome-stopovers-spain/motorhome-stopovers-spain-valencia/2530-mediterraneo-camper-area-calpe-alicante-valencia-spain?highlight=WyJjYWxwZSJd&i=calpe-2-6

If you can, I'd recommend going inland from the coast. You'll find more space and more of real Spain. Lots of small towns and villages have stopover places these days and they are generally cheap or even free for facilities. Check out the Valencia stopovers for ideas https://www.clubmotorhome.co.uk/motorhome-stopovers/motorhome-stopovers-spain/motorhome-stopovers-spain-valencia

Hope that gives you a couple of ideas but please do ask if you want specific information.

Weather should be lovely. The only thing is the days are short so it can get quite chilly in the evenings and overnight but soon warms up once the sun comes up again.

Have a great trip, obviously Spain is different to France but its way more motorhome friendly than it used to be