The B5M has a problem with motors getting hot (compared to the rear motor version) because the chassis mount blocks airflow to the motor, when the motor temp is marginal. Making one with a fan mount would solve the heat problem.
I thought that 3D printing one should be easy. It turned out to be pretty tough because with a hole for the fan airflow, there isn't much room for the structure. After lots of optimizing, I came up with a design that is durable and have them printed at Shapeways. I've been impressed with the accuracy, appearance, and durability of the SLS Nylon at Shapeways.
https://www.shapeways.com/shops/eriksparts