From what I have heard from reviews base after some use usually cool.
After 1,5 h. in Iracing base is warm, is it normal behavior?
It depends on what kind of torque levels you are running.
Usually a human feels a surface of 55-60 degrees Celcius as hot, and warm is anything between 30-50.
I would say your experience is completely normal.
Usually, my SC2 pro is cool to the touch. Not even warm. I just had one instance when training for the Nürburgring 24 when the setup they wanted to use for an AMG GT3 (in Iracing!) felt VERY wrong (super hard and heavy with far too much toe, etc.) and after an hour or so my arms were dead and the servo was boiling hot!
I asked them to use another setup even though it felt safe on their gear or belt driven low torque wheels. I really didn’t want to damage my SC2 and I wouldn’t have been able to drive for 3 or 4 hours with this kind of torque (my settings are quite strong 100% in TD and 25nM/50nM in Iracing).
So, the setup is a major factor too sometimes ^^