How can I permanently disable the car alarm?

Hello, I don't see a 4-cylinder model for that year but looking at the V6 model which probably has the same type of alarm and Immobilizer system. It really shouldn't be going off when you try to open the van using the key.

What you can try is to exit the van, lock the doors using the lock switch on the door, keep the key in your hand. This will arm the system after you close the locked door. The vans alarm system should be disabled once you unlock the door with the key either manually or with the fob.

When you lock the van does the security light inside the van start to flash or does it stay on continually? It should start to flash. If it's just staying on that means there is something still open, such as the hood, a rear door, etc.
Also, if the horn sounds three times when the door or liftgate is unlocked, it means the alarm was activated and the van has been tampered with.
So, what might be happening is there may be a bad door switch or hood switch that is malfunctioning, and that's why the alarm is going off when you unlock the van with the key. Because it really shouldn't be doing that, it should disable the alarm if the van is unlocked with the correct key. It's not like you are breaking into your own vehicle.

So, you may want to have the van looked at, if there's a problem somewhere with the security system or a wiring issue, you may come out one day and the van may not start. There could be a situation here where the security system is not transmitting and that's why the alarm is going off. Each door has its own Arm/Disarm switch in it and the driver's door switch may not be working correctly.

Happy to help. I was just wondering when you lock the van, can you see if the security light is flashing, or does it just stay "on" all the time? That would give some indication if there were an actual fault happening. When the system arms itself after locking, the light should flash about every second. Also, did locking the van using the door switch help at all? We like to help get a situation resolved, if possible, without having to take it to a shop.

If there's no security light at all then there is probably a fault in the system and that's why it is activating when you do anything to the system.