The Atlantic coast of Portugal is fairly exposed so the weather in Jan/Feb won't be as warm as in the Algarve. We were in Portugal in April 2009 and even then the weather in the Lisbon area wasn't too good. However, we then went to Figuera da Foz, north of Lisbon, and had lovely weather. We stayed in Camping Orbitur Gala (there's a review on this site) and loved it. Portuguese sites are not always known for the luxuriousness of the facilities, but the refurbished sanitary block at Fig Foz was excellent., and there's a stunning beach a short walk away.
------------- Il vaut mieux vivre ses reves que rever sa vie