Chambre Libre France in August

Do a search on Booking.com. Use their filters to narrow down what works with your needs. I am guessing your options will be somewhat limited at this late date. Yes, do check with the Tourist Authority for the towns you will visit, but I wouldn't wait until you show up there. Go online now and secure your lodgings, unless you don't have to worry about prices. Have you secured your rooms for your Paris stay, or will you go directly to a location outside Paris? August is the month when most French people go on vacation, narrowing down your options for availability.
Have never heard of Abritel. Gites-de-France is a great and very reliable site for finding lodgings (outside of Paris), and although they offer whole houses, we have found chambres d'hote with them (rooms in homes, true B and B's). Bonne chance!

Thank you so much for your quick response. I used to live in Germany and it was easy to go to the pub and see zimmer frei and I was hoping the same would be true in France. I will check out the organization you spoke of before leaving. We have accommodations in Paris and just wanted to see more of the area. Any suggestions for 2 more or less mobile 70yo? I don't want to run all over the place, just want to enjoy the atmosphere - so quality is better than quantity. Unfortunately, we are also on a limited budget which makes things a bit more challenging. Again, thank you for your feedback.

We are 82 and 83, so we do remember "zimmer frei" and "chambres d'hote" signs from long ago days in Europe. We spent 4 months in Europe in 1974 driving around in our VW bug (picked up in Wolfsburg, Germany). We would find our room on arrival, whether in big city or small village. Even in 2003 we could go to the tourist office in a town in Ireland and reserve a room ahead for our next stop (traveling by car). Alas, those days are pretty much gone. Do reserve ahead. I have reserved through Gites-de-France and Booking.com. Both companies have provided excellent service. With Booking.com just use the filter sections on the left side of the page for a town you choose, then check out all the photos and read the reviews. They only post reviews from people who have stayed in a place. With Gites-de-France the website was in French, but they may have an English language option now.

It's a bit late for finding lodgings, especially in the best-known places like Strasbourg, but I'm sure you will have success. And do try to find the website for the official tourist offices of the cities and towns. They may have some sort of lists.

P.S. Never heard of Abritel so can't comment on them.

Abritel was a French company roughly equivalent to Airbnb that was acquired by Vrbo (Expedia) about ten years ago. In France, Vrbo is not very well known compared to Airbnb and Abritel, which is why the Abritel website was maintained. I assume that you can find the same accommodation listings on both Abritel and vrbo, at least for French properties.

It is true that Abritel has a bad reputation due to the risk of scams and fraudulent listings. Personally, I have never used Abritel.

The "old-school" method for finding last-minute accommodation outside of major cities is, first and foremost, to go to the local tourist office (if there is one). They always have a list of local accommodations and can contact them for you to check their availability. If there is no tourist office, you can drive around the region and look for roadside signs advertising places to stay (such as Gîtes de France).

My parents used to ask local shopkeepers (bakers, butchers) for recommendations. Even today, this could still work in rural areas, provided you speak at least a little French.

Again, thank you for your quick responses. My head is spinning a bit, trying to work things out. I don't know France at all. I spent 9 years in Germany and feel confident there. This trip is definitely pushing my comfort zone. I guess I need to purchase rail tickets before purchasing a room. I'm sure no matter what, the experience will be well worth it and there will be a multitude of surprises awaiting us.

Our most nightmarish hotel experiences in France were when we tried to book as we went; the internet has totally changed the scene from 30 or 40 years ago when the tourist office at the train station was an easy place to book rooms. I would never travel now without booking ahead. If you want flexibility then have a list of places and book a day or so out -- but it is not uncommon when we have done this for us to go through half a dozen on the list that are booked out the day before. Consider booking a base so you aren't touring with your luggage in the car and day trip into the area from a pleasant town in each region you want to visit.

I think you will find the necessity to prebook your lodgings goes across all of Europe (at least western Europe), Germany included. As mentioned above, the internet has changed the way rooms are found and booked. Your best bet for the "old school" method is to go to smaller, less well-known towns. Provins and Strasbourg don't fit into that category. Provins, though smaller, is well-known to tourists, and Strasbourg is quite large (and wonderful as well!)

What are your dates and how many nights on the ground do you have? Anything in particular you are interested in....art, history (recent or medieval e.g.), scenery, wine-tasting, culture...? Will you be renting a car when outside of Paris?
Are you spending any time in Paris? If so. how many nights? August in Paris is less crowded in some ways because that is when many Parisians go on vacation.

Also, depending on where you plan to go, you may not need to prepurchase or reserve your rail tickets. It depends on your itinerary. Some places may just be commuter-type trains with frequent schedules and short travel times.

Regarding Provins, the tourist office offers a list of accommodations:

https://provins.net/en/prepare-your-trip/where-to-sleep/

They also manage a list of gîtes (holiday rentals), website in French only:

https://www.gites.fr/tourisme_proximite_office-de-tourisme-de-provins_provins_22357.html

As you know, Provins is a fairly touristy town, with the Medieval City of Provins inscribed as a Unesco World Heritage site. Furthermore, since it is close to Paris, it is likely to be quite crowded in August.

Strasbourg is even better known for international tourism, so it will be the same in August:

https://www.visitstrasbourg.fr/en/organising-my-stay/places-to-stay/

I think you will always find a place to sleep at the last minute, provided you are willing to accept what is available without being too picky in terms of location, comfort, and price.

Regarding train travel, long-distance routes are in highest demand in August, especially from Friday through Sunday evening, when people are heading off on or returning from vacation. Regional lines connecting small or medium-sized towns generally have no availability issues. In fact, they often do not offer seat reservations, so you can simply sit wherever you like.