I pan to have an enclosure with the battery, but worry about the temps inside the enclosure in the sun. How heat tolerant are the cubecells? If temps reach 120 to 130 F (48-54 C) or more, will that damage the board?
48 ~ 54℃ is fine for CubeCell.
CubeCell can working stable between -20 ~ 70 ℃.
would care more about the battery at that temperatures.
What battery type are you using?
I am using LifePO4 batteries because they are more heat resistant.