If you decide you wish to help the outfit by providing Sunderer cover, there are a few things that are useful to know.


Upgrades

You can only use one upgrade in each slot at any given time.

Advanced Mobile Station (Utility Slot)
The prime use of the Sunderer is to provide a spawn point. It can be used for transport, but in most cases this is of secondary importance compared to the ability to respawn. Death can be quick in Planetside 2 and the ability to respawn in a nearby location can often be the difference between taking a location and giving up on it. As such the AMS upgrade is really a must. It costs 50 certs.

Negative Phasing Shield Generator (Utility Slot)
If this could be combined with the AMS it would be incredibly powerful. As it is the use of a Sunderer with this upgrade is rather short. The best way I can think of to use this type of Sunderer is for breaching the inner shield of a base to gain access to the inner vehicle spawn so that it can be hacked and an AMS Sunderer built. Note however that the automated drive away from the vehicle spawn often chucks the vehicle through the inner shield which is less than ideal. This upgrade isn't likely to see any use outside of organised play.

Smoke Screen, Radar and Fire Suppression System (Utility Slot)
These upgrades make more sense on other vehicles. Compared to the AMS upgrade they have very few benefits.

Vehicle Ammo Dispenser (Defensive Slot)
In many ways the next most useful upgrade. This one is not essential but it is very useful. Without at least 1 ammo resupply upgraded Sunderer it becomes very difficult to sustain long range tank battles. Short range tank battles are very lethal and will lead to a lot of lost tanks. As such if the outfit wants to engage in prolonged tank use, we need 1 of these.

Proximity Repair System (Defensive Slot)
This one is less useful. It can help in tank battles, but for smaller engagements it is often possible for supporting tanks to retreat and heal via engineer. This upgrade doesn't provide something that would be unavailable elsewhere like the AMS or the Ammo Resupply upgrades.

Stealth (Defensive Slot)
This protects against radar spotting. It also increase lock-on time, but that is less useful as the Sunderer is often immobile anyway. In my experience this can be quite useful for avoiding attention. If someone sees a sunderer at a distance without the red arrow over it, they are much less likely to call it out as an enemy. The less attention the sunderer draws the longer it lives and the better chance the driver has of hiding it behind a building or some rocks.

Nanite Auto Repair System (Defensive Slot)
An auto healing bus. Damage disables this system. If the bus isn't taking damage, an engineer can heal it pretty quickly. This upgrade may have a use if the driver wishes to wonder away from the Sunderer and leave its survival up to chance. It also might be good for a mobile non-AMS Sunderer that is constantly roaming around relying on its turrets. Any other type of Sunderer use is not going to get much out of this upgrade.

Blockade Armour (Defensive Slot)
More armour. The ability of a AMS sunderer to survive is often more down to the ability to runaway from or out heal the attacker. More armour doesn't really help much with either of these things.

Mine Guard (Defensive Slot)
At the present moment mines are not a popular upgrade. As there aren't a lot of mines about, it is therefore less useful to be able to get an upgrade that protects against them.


Tips

Squad Transport
Normally at the start of play the Sunderer won't be used for squad transport. You might be carrying 2 people around on the turrets but that will be it. Instead everyone else will bring a tank. This occurs if we start out at the warpgate. As tanks die off people start to stack up in Magriders and begin to want Sunderer transport.
You are expected to at least ask if anyone needs a ride before driving to the next objective.

Quantity
We don't need everyone going Sunderer at the same time. We will get through quite a few Sunderers in a night, so be prepared to wait for a call for a Sunderer before getting one out and make sure everyone knows you are getting one.
Generally we want 1 Sunderer per 12 man squad.

In Play
The driver is often expected to remain in or near the Sunderer. A Sunderer will live a lot longer if the driver is prepared to reposition (run away) when enemy tanks show up. Alternatively the driver may need to be an engineer repairing the Sunderer while under fire. It is often possible to hide under the Sunderer while repairing it (if spotted you will be shot though).
Facing matters. A tank firing on the rear of a Sunderer can kill it very quickly. Equally the starting Sunderer turrets are effective enough that the Sunderer can win when firing on the rear of a tank (although only if the tank misses at least some of the time).
Try to find a good spot to allow people to flank from based on the position of other deployed Sunderers.

Riding the bus
If you're in a turret position you need to keep an eye on your ammo.
Although the turrets are quite effective against air targets, it is generally a bad idea to waste ammo on them if they are at long range. If they have clearly spotted the Sunderer or are attacking/defending the same position then they are good targets.
The same applies to tanks. If the tank hasn't spotted the Sunderer, then we would much prefer to sneak by it.
If you are not in a turret position then your only job is to be prepared to jump out and defend the Sunderer should it blunder into something it can't handle. Tanks are the prime threat to the Sunderer, but Liberators and massed interceptors (Scythe/Mosquito/Reaver) can also be dangerous.
As such switching to a Heavy/MAX are your best options. You should do this before getting into the Sunderer. When under fire the Sunderer can't afford to stop to give you access to the terminal. It is much easier to jump out and switch to engineer to help repair the Sunderer than the other way round.