The problem isn't the spawn points.......
It is the players..
If you can get GVers to push a base, the first thing they want to do is camp the spawn, so they can run up their score/kills.
Why is not the first plan (and best) to take down the hangers??? HTC would not need to try and fix spawn hangers then. He would be able to use his time making new planes or something.
CAV
As already expressed, it takes far too much energy to drop all hangars. A single T-34, properly driven can eliminate all guns and effectively hold down the spawn hangar, while calling for a single M3. That means two players to take a field and adding an enclosure does little to tip that equation, I must confess. All I have to do is enter the enclosure and the chances of taking the field are immensely increased. Not only can he no longer spawn and fire on my M3 or troops, he is trapped and must deal with the double threat of my butt shot and dropped ordinance, from which it is very difficult to escape. The shelter is in effect a death trap.
I think being able to chose the direction you are facing when you spawn would be a nice compromise to the spawn problem. When camping a VH it's ducks in a barrel because the Vehicle and turret always face the same way, so if you get behind the hangar, the vehicle inside has to spin the turret 180 deg to shoot. That simply takes too long so the vehicle has no fighting chance. This is similar when camping a Spawn in the open field.
My proposal is add an orientation selector to one of the open squares on the clipboard spawn controller. I don't think there is a spawn that uses all 9 buttons. so the routine would add the orientation selector to an open slot. The selector is an arrow with a button at the end that you click and grab, then drag around the circle. Then when the spawn location is picked, the vehicle spawns facing in the direction of the arrow.
This gives the spawning Vehicle a fighting chance to correct and turn on repeated spawns if the spawn is camped.
This is a proposal I have considered and endorse.
If you must use an enclosure, you have to give it defensibility. The inner walls should be sloped, so a defending tank can escape from any angle, while the outer walls should be steeply sloped to prevent incursion. There should be a small barrier on the back to protect from ranged camp shots and it should be fashioned to allow fire points. Finally, it needs to allow unrestricted view of the map room from the spawn position. See below:




If you changed the style to something like this and allowed for reversed spawning, it would greatly compound the difficulty of setting camp on spawn hangars, without unduly complicating base defense. This enclosure should work at all fields, perhaps by raising the barrier to accommodate ports.