Here is how I did mine:
I used those sonic tronics spring loaded hinges.
I used 2 per side and one non springed hinge.
That way the door is loaded to open.
Then go to your local bass pro or any place that sells fishing line.
Get some of the basic light weight stuff.

you will need to drill a small hole on both sides of the gear doors.
one hole per side.
Firmly attatch one side via glue or washer or big knot.
Loop the line BEHIND the gear leg and feed it through the hole on the other door.
Retract your gear, the string will catch the fishing line and want to close the door.
When the gear is up you can pull the string taught and tie off the other side.
It is now the exact length to close the door and remain shut.
as soon as the gear starts to come down the string will loosen and alow the door to open.
per the spring loaded hinges.
Fishing line is nearly invisable and is slippery and will slide along the gear leg.
You can also set the amount of gear door will spring open with a line from side to side
in FRONT of the leg.
This prevents the door from hyper extending when open.
It took me many different ideas to come up with this one.
It is simple and it works
Patent Pending.
Greg