I believe adding mech-style weapons to turrets is not a very good idea.
The mech weapons are relatively OP already and the turrets have no ammunition limitations.
In addition the ion rifle does not work reliably against the turrets, if you cant take out the APC with the ion (which is quite often not the case)
But the current turrets are a joke.
A skilled person can easily take out a turret without ever getting hit.
To make turrets a larger threat we have to look at the two most common tactics to take out turrets:
Fire and Duck
The "Fire and Duck" tactic uses the delay between the turret coming out of the ground and starting firing to get a few shots into the turret and then ducking back into cover before it can get a shot in.
You can repeat that indefinitely until the turret is taken out.
The counter for that is relatively simple: increase the time it takes the turret to come out of the ground and start firing.
Or possibly give it a "shield" that recharges once it goes back into the ground and can take a shot or two.
Lockerblock
The "Lockerblock" tactic uses lockers to block the firing path of the turret. By just pushing the locker forward and walling the turret in with lockers, the turret wont fire on any human mobs
To fix this the turrets would have to be adapted to disregard dense objects that are not anchored in its firing calculations.
And it would be important to check if the objects deteriorate and disintegrate after sufficient hits by a weapon.
Crawl and Hit
I am not sure if that has been patched already, but this tactic is essentially a adaptation of the "Fire and Duck" tactic.
Crawl up to the turret (it wont shoot you while you crawl), get up and hit it as it emerges from the floor and lay down again before it starts firing.
It is possible that this bug has been fixed already, if not the fix is relatively easy: Continue shooting mobs that arnt unconcious (possibly with the limitation that they have to get into a small radius around the turret)
As a final note: Some of those tactics outlined here use bugs or oversights.
If you use them ingame and get bwoinked as a result, its your own fault.
You have been warned.