As others have said, it is the nature of the PUP beast. Lack of insulation really hinders the cooling effect. Also, the tent type material doesn't help. Get the gizmos and reflectix. There are different types of gizmos and taking the measurements are easy. Your beds and dinette prob run you $200. Well worth it even though they are a bit of a pain to put on and off. And the reflectix you buy in a large roll and cut to size. My local homedepot and lowes doesn't carry it in stores. Hopefully, your does. If not, WWW. And you may not need to put them in all your windows every time. Sunny side helps obviously. A bonus, they keep it darker inside and allow my kids to sleep later
You will see a big difference with those in place. Good luck.