Just what I've been looking for: A survey of what British soldiers thought of the country and the people of Spain and Portugal while living cheek by jowl with them (via billeting and campaigning). Chapters include To the Peninsula (preconceptions), First Contact: Lisbon, Landscape and Climate, Billets and Hospitality, Searching for Civilization, The Religious World, and 'Dark-Eyed Beauties.' The culture clash is vivid with great details.
Missing was mention of British women, wives and camp followers. It does seem like the presence of hundreds or thousands of one's countrywomen might have some effect.