Lots of things to bear in mind ......but people do do what you intend.
You do not say if you have towed in Spain before or whether at the time of year you mentioned.
What will your route be and your destination?......Spain is a big country!
Many Brits think of ......Sunny Spain........ and it
is sunny on the south coast during the months you mention but you have to get there first.
This picture was taken north of Madrid on January 30th 2014 on the way south.
The temperature was -5 deg C at an altitude of 5000ft.