Don't see too many basements around and have been told they are a bad idea due to unstable soil. I'm looking to build a attachment to my house on wheels and want to build a basement under my addition. Nothing but red dirt on my property. I'm looking to build a basement that doubles a a storm shelter for my tornado magnet of a house. My house moght be a modular vs mobile but it still came with wheels.

If clay is the issue, what needs to be done to build a basement with walls that won't crack?

Red clay swells with water, shrinks when dry.
The constant movement of clay in the soil is apt to crack basement walls fairly quickly.
Then they will leak badly.
It took 25 yards of concrete to build my patio/storm cellar in red clay.
I had cracks from the beginning and even when I sold the house 4 years later.
I was using water stop concrete patch fairly often.