I like it, should work out nicely, only issue I'm seeing is the length of stroke needed. The trim pump has some great control but not much stroke. Shorting it to lift that distance and having enough mechanical advantage to start going up I'm looking as the main point. Another thought with the hydraulic cylinder you will need an access panel to get at it if it fails in the down position.
A engine hatch lift has a drive which can extend 18 to 24 inches, and capacity in the 90 to 115 Kg. The hatch actuator needs a bit more room due to the size. I removed one off my Cruiser because it could be no longer used after the motor repower. It has a bar mechanism that allows the hatch to be raised manually or with the motor. Will get some pics and show how it works.
http://www.cpperformance.com/p-30-18-inch-stroke-electric-hatch-actuator.aspx
Another method is a winch cable. The winch would be mounted behind the bulk head at least half the distance. The cable could be attached to the center. So gravity brings it down and motor up. Having a cable would also allow the lift to be manually raised if needed. Issues would be the cable would be seen coming out of bulkhead when lift is down. Could mount it down low, but then I see the need of some sort of radius lever to apply leverage.