If it is in full sun with no shade at all, it will have a hard time keeping it in the 70's, low to mid 80's is doable. If you have some shade, it is doable.
There are some things you can do that will make a difference. Bunk end covers (Popup Gizmos) will help as will putting Reflectix in the bunk windows. We close the curtains on the bunks during the day if we aren't going to be in them and that seems to help keep the AC in the main part of the Pup. Once the temps cool off some, we will open them back up so it isn't stuffy at bedtime. We also have some fans that we can use as well. Overall, it stays comfortable, especially compared to the outside temp.