I advice you on turn 1 to run to the largest room's roof (unless you start at the very other end) and camp there.
I finished an impossible march landed supply with no damage at all by:
brought: a rocketeer, a scout, a sniper, an infantry, a gunner and an assault all SPEC. Rocketeer gets SMG, sniper gets sniper rifle and a medkit, scout gets marksman, gunner gets LMG and medkit, infantry gets Battle rifle with laser sight. 3 soldiers additionally brought AP grenades and 3 also get flashbangs
I got a lucky LZ; directly beside the largest room, so I climbed to the roof of that.
I heard at least two Chryssalid pods. So now my priority is to kill those pods first, if possible.
I stayed on a roof without doing anything for 4 turns to see if the nearest pod was roaming. It was not.
I moved around the roof to hear pods over ~16 turns. I heard 1 static Sectoid pod, 1 static Chryssalid pod and 1 roaming Chryssalid pod (dangerous!!)
so my first activation was the roaming chryssalid pod.
I did not overwatch. Everyone steady aims. (March aim is horrible.)
after finishing the roaming pod in one turn, I proceeded to kill the two static pods near the roof after waiting to see if any roaming pod will come by. I also discovered a static chryssalid pod hiding right outside the small door to the large room accidentally. Luckily everyone steady aimed the turn before so we quickly disposed of that surprise chryssalid pod with one AP grenade and several follow up shots. Missed one 94% shot but still made it through with the others all getting really high aim shots. If we didn't have steady aim we would have been devoured by the Chryssalids.
when dealing with/activating Chryssalid pods, move your assault first. He can run n gun after being surrounded to be useful.
My first three pods were Chryssalid pods. After jumping down the roof with my assault to manage the Chryssalid pods, I swiftly went back to the center of the large roof and reloaded to prevent any accidental roaming pod coming in.
my next pod was on the edge of the roof and a roaming sectoid pod on the ground. Upon activation they escaped so I retreated and hear where they went. There was an accompanying drone that i easily disposed of with my steadied sniper.
somehow they went all the way into the large room.
this is important: because I didn't hear ANY silent pod while above the big room, it is OK for me to open the big room and assault the sectoids. Otherwise it is far too dangerous.
after killing the sectoid pod I went to deal with the static sectoid pod on the other side of the big room after positioning myself to fully surround it. When aliens are surrounded upon activation, they frequently bug out and their AI don't know what to do and therefore choose bad positions.
after that I heard 2 floater pods all the way across. I used the center roof, which is extremely dangerous, but allows for height advantage over floaters.
unfortunately the static floater pod that I heard was a bizarre split pod so I had to retreat all the way back.
at the same time another floater pod roamed in so I'm now flanked on the left and right side of the roof.
this is important: I left some soldiers on the roof facing the center of the supply corridor with half cover OUTSIDE of LOS from the other end facing the command room. A scout constantly moves up and see if any floaters are coming and an infantry jumps down to see if anyone is flanking from the other side of the roof facing the ground.
by this way I killed two floaters (six left) before I had to retreat.
alien AI is not good at pursuing so I went back to the top roof above the large room and sniped the floaters one by one. Be careful of flanks however. Leave two spotters somewhere on your flanks.
now leaves the command pod. I hear them in a strange position.
while on the left door of the command room, I hear the cue being not directly to the center of the room, but towards the edge. This means I cannot flank them from the ground-facing door because there is a possibility that some of them are outside. So I flanked only from three sides, being very careful to hear the audio cues before any movement.
sure enough, two outsiders are outside the room. Upon activation, four outsiders including the boss outsider bizarrely with 10 HP (but with LR!!) went behind the computer. Two outsiders jumped down to the ground. So a steady aimed shredder rocket and one AP grenade killed two of them in one turn. The other two were left with 2, 3 HP but unfortunately all my other shots (all four shots with 60%+ on three and 40% on the second battle rifle shot missed!!!). I didn't move from position at all because I know the ground outsiders cannot flank me in one turn and I flashbanged the remaining two.
next turn the remaining two ran out towards the ground side and took cover on the half covers right outside the room. I cannot pursue them because the ground outsiders can now flank me in one turn possibly, so I left them alone.
since outsiders cannot climb roofs, and since you can't see the roof from the ground at all unless you stay out of cover (painfully remembered when I was once on the reversed role with thin men), I went on the roof and camped there.
I left the useless gunner to run somewhere far away. Sure enough two of the outsiders ran towards him (seen by yellow-move tiles spotting).
this leaves two outsiders on the ground. When aliens can't see you they know where you are but sometimes leave cover, so I waited until they left cover and killed them with a rocket and two shots after jumping down.
the gunner climbed a roof and ran back to the command room through the roof and there's nothing the trolled outsiders can do about that.
dispatched the remaining two outsiders in a similar fashion, and accidentally discovering that outsider pod leader had LR when accidentally over watching instead of steadying.