Hi hopefully this may help
Not been south of Ovar so cant help between Olhao and there but at Ovar there is a Municipal site on the beach, follow the Campismo signs from the IP1/IC1 (IP1 Junction 17) its lovely there and the town is good too
Near Porto in Vila Nova de Gaia there are 3 sites within 2 miles at Matosinhos if you are on the IP1 cross over 2 the IC1/A17 and come off N109 Espinho follow signs to Madalana You will see the sea front drive along and choose site ! There is a super bus service to Porto & also to the Port wine caves which are 10 minutes away by car/bus. Porto is a favourite of ours for its mix of old and new, river and sea, but thats just us.
We have gone in and out of Spain on 2 roads, the first which s far prettier/scenic is the IP4/E82 from Porto to Braganca There is a huge hill at Vila Real which is 10/15 mins solid climb. From Braganca follow the E82 into Spain,onto Zamora-Valladolid-Burgos etc The other route is the IP5 to Guarda linking with E80 into Spain to Salamanca-Valladolid etc.
There is a site just outside Valladolid Camping Cubillas which is fine for an overnight, the bar is a bit rough and ready but its ok If you go via Braganca there are a couple of sites there and an old citadel if you like that sort of thing
The first IP4 route has some stunning scenery/lakes and beyond Vila Real is as easy as the other route
Rather than carrying on,dont want to bore you ! If there is anything else you want to know please dont hesitate to ask
Hope your trip is good, Simon