Hi @AFCA161 welcome to OG!
Nicely built box…!
Yea definitelly check the humidity and preferably use hygrometer.
In my experience adding humidifier helps especially with young plants and seedlings (rasing to ~60% RH). The need to add humidity in later stages decreases.
Just for the reference… Link to FAQ about humidity: What range should I maintain for my growroom humidity and temperature?