It 's worth buying the recently published Seventh Edition of the RCC Pilotage Foundation "Atlantic Spain and Portugal" if you are cruising in this part of the world. Clearly illustrated and bang up-to-date.
In addition to OCC negotiated discounts it is possible to buy a "Pasaporte" which gives berthing discounts of 15% in several marinas in the area. Cost: €5. Amazing value.

Richard Lassen, aboard Oestara www.followingwind.co.uk Callsign: oestara PIN: 3624

My experience over many years is that the Customs Officers are always most polite and helpful. They fill in a form in duplicate. A copy is given to the yacht which is valid for one year and can be shown on a subsequent visit.
They have a difficult and dangerous job to do including large drug hauls on foreign yachts several times every year, and any attention from them should be welcomed.
I agree that three visits in one week is too much and may have been a mistake, but nevertheless they are all powerful and every respect should be shown.
It is worth going out of your way to meet them if they are berthed in a marina and having a chat. They may even show you around their amazing patrol boats.