Here is the mod I have done to stop the gear doors opening. I used a Robart 165L cylinder, 3/8ths diameter by 2.5 inch stroke. I used a cut down plastic aileron horn which has three mounting holes as the fixture to the door. It is bolted on & also epoxied. The cylinder has a clevis attached. The distance from the clevis pin to the inner edge of the door is one & seven eigths of an inch. The top of the cylinder is mounted on a short extension level with the top edge of the existing cylinder mount. The cylinder is almost vertical to the door when closed.
In a test at 80psi the door on the unmodified side opened with just a touch of a finger. On the modified side, I would have broken the door if I had pushed any harder. This setup gives great mechanical advantage. The operation of the retract sequence is smooth & the cylinder does not interfere with the wheel going up & down.
Sorry about the quality of the photos. I used my phone camera.