No... one of our strings has not broken. But, am saving that info for the "what-ifs".
The longest we kept an RV was our Itasca, made by Winnebago was five years --- and we NEVER had a string break. I expect these to last too.
On tightening your string, Sharon--- do you have a deal on the wall that looks sort of like a "bobbin" from a sewing machine? You just pull on that string that is loose, stretch it out and take another wrap around the "bobbin holder"... Pretty easily done if you have that type set up.
Also we had a couple of small spots on our day/night shade by the table, and I sprayed it with Shout.. rubbed on the spot until it was gone. It cleaned off beautifully, leaving no discoloring or water spot.
Happy Traveling!
Joella