I have two Jack Russell's - and although they are small they are fast and after a year or two the flaps will start to fail (usually loosen to they keep falling off or snap). 

Design Considerations

• One side is flush on the build plate to minimize supports.
• Supports a 6x4mm magnet at the bottom

Printing

• Recommend PETG as it needs to flex, not to mention it will be exposed to UV. 
• 50% Infill (for weight and strength)
• 0.4mm nozzle is fine