Metal flex duct is better than the "dryer hose" you are using now. Anything (like ribbing) inside the duct that reduces or eliminates laminar airflow causes resistance, which causes the static pressure to exceed the capabilities of the motor.
In addition, you need to be careful of exhaust hose length--for the same reasons. Check your instructions to see if the booth has a designated maximum hose length. Last, try to avoid a lot of bends in your ducting, especially of the 90-degree variety.
By the way, flex duct can usually be found at your local Home DIY centers, and possibly at home appliance stores.
Good luck with your booth.
Gip