I spent last winter in Spain, then bought a house (in Spain) and sold the van. My observations from travelling, in no particular order:
The Spanish are keen on campervans and aires tend to fill up Friday afternoon then empty out on Sunday. If you're staying on aires I'd suggest getting there by midday Friday and not leaving until Sunday, finding a park up on a Saturday can sometimes be tricky.
The middle of Spain is known as "empty Spain", everyone left to find work in the towns and cities. You won't have to drive too far out of Bilbao to find it and Empty Spain can be a depressing place, there's a government ministry set up to try and find solutions. What looks like a nice place to stop on Park4Night can be a village with 3 elderly residents, a mobile supermarket that stops once a fortnight and a bar that closed twenty years ago. Spain suffered with the financial crisis in the late 80's and is full of half built flats and houses. Put those on the edge of a crumbling village with very few residents and it can be a disheartening experience.
Once you find the bits where people live, Spain changes into a vibrant, happening place. There are so many places to see and things to do you'd need a couple of lifetimes to get it all done. The Spanish people are lovely, friendly, helpful. As usual keep your wits about you, especially in the bigger places, there's no more crime than anywhere else though and I feel very safe here.
The country is mountainous and can get it's share of snow, something to be aware of if you're driving around in the winter.
I've been driving in Europe for many years and have never bothered with headlight beam adjust stickers. I've never been stopped or flashed by other drivers at night. You should carry 2 warning triangles and a flouro vest for every occupant of the vehicle. I think there's a law about having a spare wheel or being able to fix a puncture but that's something I'd recommend everyone has. Be aware of the speed limit for your type of van, the Police aren't shy of handing out on the spot fines.
If you're using campsites in the off season an ACSI card might be useful.
There was a thread about hose connectors a couple of weeks ago, bring all the stuff I mentioned on it. A means of filling the van water without being next to a tap is handy too.
If you're using electric hook up get a 2 pin adaptor for your 3 pin lead as mentioned above, you'll probably definitely more than likely use it.
The beach park ups can get full very quickly, which leads to illegal parking, which leads to the Police knocking on the van at 4am with an on the spot fine and being told to move or you'll get another fine. If you fancy the seaside, and who doesn't (me actually, I've no interest whatsover in beaches) talk to other people you meet and get tips from them as to where is full, good, bad.
I've no opinion or advice on Portugal, it does look very nice though.
