Please limit the number of defense turrets in any given location a-la offense turrets, cuz ATM all aliens need to do to win is build 6 offense turrets spam it with 6 defense turrets and the only way to shift them is have yer whole team bombard them with grenades or build 5 siege turrets, meanwhile they are off attacking your installations knowing full well their little base is nigh invulnerable. Grated siege turrets can be set up at all key points to insure they cant build these little bases but by the time they become availible half the map is already dotted with these little bases.
Another issue to note is that with even 4 of these defense turrets set up it is too easy for aliens to stage constant hit-and-run attacks using just their acid rockets. Fades simple whiz around the corner bombard the area with acid rockets retreat to their base and their 6 offense turrets protect them in the 5 seconds it takes the defense turrets to heal them. two faades can easily take down a whole base in this manner.
An alternate or possibly this could be use in conjunction with limiting them, is to have it so they can only heal one target at a time. This would help in my opinion to lower the effectiveness and invulnrability of these bases since they would require at least SOME measure of player-interaction to prevent their distruction. At present this is a rather large unbalancing issue since turrets have to be repaired, while leaving the marine guarding them open to attack and unable to defend himself.