This is what I used and am very happy with results.
Bansbach Easylift - Part # A1A1F50-100-287/600N. Costs in 2019 was $62 each.
www.easylift.com
Three things I like about it:
1. Very strong! Before I installed windows and hardware, was afraid it was too strong. But after added weight of windows, door lock hardware etc... it works great.
2. It is "self dampening" to slow the opening of the door in the last few inches of lift. Be sure to install fat side up (door side), or the self dampening will not work properly.
3. Stroke length allows me to grab door while standing on the ground when door is open. A friends RV-10 has another brand, and even at 6'2" I can't reach the open door from the ground to close it (it's too high up). Mine has just enough length to open fully, but not too much that I can't grab the door to close while standing on the ground.