Props have a rotational direction and need to be pusher and puller type- can’t be turned over.
Between the motor and ESC there are 3 wires. Plug them all in any-which-way.
Run it up and check motors rotation (NO PROPS attached!)
If motor is rotating the wrong way - swap ANY TWO - ONLY TWO of the three wires
EG Determining Motor Direction - YouTube
A 9 fingered drone builders tip:
No props mounted - safe as houses
Props on motors - use extreme caution-know when armed and disarmed
Have you looked into the motor bearing construction? The motor has to react the thrust force of the prop. A pull type and a push type require the force to be reacted in opposite directions. Be careful not to push a motor that was set up for no axial loads, or for pull axial loads only.
What are the issues with the electric motors if they get rained on? Will they short out and have to be replaced? Is the only option not to fly if there is any chance of a rain squall?
Others may have more information, but the motors are probably not the problem. They are just continuous coated wire (that’s what melts when they get hot and a short gets made). There are various solutions to making the ESCs water resistant. But I would think the biggest issue would be that your glider would get wet and less efficient, perhaps even to the point of falling out of the air. Plus the wind once the rain squall hits…