Flying it as a sailplane,i.e: climb and glide, you won't need any vents. Motor runs are short and minimal heating will occur. Hotliner style flying you would want some cooling. I'm running 800+ watt jobs with no vents and it's not a problem.
The motor is not an inrunner BTW, it's a outrunner in a case like the MVVS sailplane motors, they call it a inrunner/outrunner. I have three of the MVVS motors and while a tick heavy they are nice for tight nose applications with the motor wire connections mounted on the rear casing. No wires to pack away under the motor and get wrapped up in the spinning rotor casing.