Hello,
It will be just enough room.
They would appreciate the tank to be in a vertical position and will enjoy climbing to the very top.
One benefit of water in a vertical is...... it will ,likely, have less water to keep clean
They don't need much water. Keep in mind that all water sources -for soaking -needs to be kept as clean as possible.
I clean 4 water saucers every day, they get disgusting! It's amazing how much slime gets in them in 24 hours.
Plus, they will only use the , 'floor' to come down to eat and soak--- and then go right back up to 'hang out'.

Enjoy your build.
Lynn