A good chunk of people choose August as their preferred vacation month; not all people have the privilege of taking the full month off (most companies require that employees take some vacation days at other times of year to take sure they’re still getting work done on the summer months), and some people can’t even go on vacation, but those who do go like to take a week or two either in July or August to enjoy themselves in the ways they see fit.
Some people take it to the beach, others go to the countryside (August is also the month chosen by many emigrants to return to Portugal to visit their families, which means a big influx of people to small towns and villages around the country), and many just turn to nature to find a bit of both.
For that purpose, we have [os] parques de campismo, which are multipurpose camping sites. Some are near seaside or riverside beaches, others are perched on hills, and they may vary according to the services provided: some have build-in infrastructure (such as bathrooms and public showers), others do not; others also work simply as trailer parks for people with RVs/caravans, others have bungalows and a few more will have the common wilderness areas where people can actually camp outside with tents.
You usually have to pay a fee to enter the site, but the experience is certainly worth it. I’ve never had the opportunity to do anything like this, but I’d very much like to try it in the future! If you ever want to plan a camping trip to Portugal, you’ll find many websites dedicated to letting you know where the camping parks are and what facilities they have.
Since your weather is better during a larger part of the year, you can even plan your vacations in the spring or in September to save some money (your plans may also backfire and you find yourself inside a tent while it’s pouring rain outside). In any case, I hope you have fun on your travels!