Love inland Portugal in the North. Coimbra has a municipal campsite on a bus route into town. Was fine out of season but not sure how much/how crowded at this time of year. Used the rural ACSI sites mainly. Would be interested in what you find in damage after the tragic fires of last summer. A couple of the sites we stayed in were in the middle of affected Eucalyptus forests.
I'd recommend going in on one of the main motorway routes that have an EasyToll pay station a few KMs inside the border where you drive up to a numberplate recognition system and swipe your credit card. The automatic camera motor way tolls will then log you and bill your card automatically. Where there are toll ports go through the manual payment - the automatic payment channel is only for vehicles with transponders, and it's not worth the faff to get one of these.
Locations are (from North to South, clockwise around the border):
· A28 - Viana do Castelo Service Area;
· A24 – at 3,5km from Chaves/Veribn border;
· A25 – Alto de Leomil Service Area;
· A22 – next to Castro Marim/Ayamonte border
which I've cut and pasted from here:
http://www.portugaltolls.com/en/web/portal-de-portagens/home
We've used the A25 one.
It's a pity this restricts you to a few crossings but the simplicity once you're in Portugal, and the lack of need for advance planning, make it worthwhile for a typical holiday trip.