Compared to the shock from actual play, I doubt the stress from temperature variation does much to a racquet frame or strings. Composites with epoxy and carbon fibers are very robust.
String tension will vary depending on temperature and that's why we have multiple frames strung at different tensions.
If we look at the big picture, the strings can handle a wide span of tensions so they will not be damaged by temperature variations.
The technical problem with bags is that we will get a greenhouse effect if they are sitting in the sun. The temperature will be higher inside the bag than the outside. It will probably be better to open the bag to cool the inside or keep the racquets in the open. If you pick one racquet and start using it, it will equalize to the surroundings anyway regardless of the conditions inside the bag.
Natural gut and humidity is another thing.
String tension will vary depending on temperature and that's why we have multiple frames strung at different tensions.
If we look at the big picture, the strings can handle a wide span of tensions so they will not be damaged by temperature variations.
The technical problem with bags is that we will get a greenhouse effect if they are sitting in the sun. The temperature will be higher inside the bag than the outside. It will probably be better to open the bag to cool the inside or keep the racquets in the open. If you pick one racquet and start using it, it will equalize to the surroundings anyway regardless of the conditions inside the bag.
Natural gut and humidity is another thing.
