I'm trying to make a hollow sphere a player can enter and cause to roll around, but the physics/collisions are a problem.

Think a giant fishbowl with no flat base. Character enters the opening, moves around causing the bowl to move around as well due to shifting gravity. I believe I've dealt with the model already. I haven't been able to get mesh colliders to fit to the inside of my space as well as the outside so I'm guessing I'll need to use scripting for this instead but I'm not sure where to start.