I am going to assume you will be entering France via Calais, as we prefer this, so head for Rouen , good free roads all the way, choice of Pay Motorway if you prefer,plenty of Aires and free camping on this route, get the Vicarious book "All the Aires France " very easy to use and all in English,after Rouen head for Le Mans, Poitiers ,Bordeaux and Bayonne, again many Aires open on route even in winter most if not all free , but sometimes water will be off so get it when you can,toilet dumping will still be available.cross into Spain at Donostia san Sebastian,head for Vitoria Gasteiz [free Aire ] Burgos [Aire ] Zamora. then you decide if you are going to enter Portugal around here, but if like us you want to head South carry on to Salamanca ,Casares, super old town well worth a few days great at Christmas time and a free Aire, on to Valverde de Camino another great stopover Aire free and a nice town to explore.Carry on until you meet the A49 E1 free Motorway going into Portugal , you will cross a bridge on this Motorway that is the Border, turn off here for Castro Marin and you are then on the Algarve, lots of other routes but that is our preferred one at the time of year you are planning.May see you on route.