If in your plane the doors keep open when the gear is in down position, you just can use a single channel without sequencer, only needed 2 electronic valves. Set a"servo slow down" function on the TX and connect both valves to this channel. Adjust the trip point of the valve that operate the doors at 10% of travel, and the trip point of the valve that operates the gear at 90% travel. By adjusting the time of servo movement onthe TX you can adjust the delay between the operation of the doors to the operation of gear.
Gaspar