tax autonomo freelancer - offshore company? (Barcelona)

Hi there,
Does anyone have any new / relevant info on working as a freelancer here in Barcelona?
I know the law changes all the time, usually for the worse.
I am a freelancer and work with clients in England, Australia, New Zealand, Brazil and Spain.
Could I get around the painful autonomo social security payments by having an offshore company?
It's just that some months I earn zero here and that can be for 3 months. And others I earn decent and can afford to pay it.
Appreciate advice!
Thanks