No matter the brand, alarms will still install basically the same way. DEI as well as most other manufacturers recommend their products to be installed by a professional because of the complexity of newer vehicles and also to prevent any damage to the alarm unit.
It's best to install the main module as discrete as possible to make it harder for thieves to locate and disable. Splicing, routing, and insulating the alarm wiring the same way as the factory wiring also makes it harder for thieves to distinguish between the alarm and factory wiring. As for the siren, mount it as high as possible so it can't be reached from underneath the truck. Keep it away from high heat sources and make sure it isn't pointed up so that it doesn't collect water in the horn. You can wire in additional sirens, but you have to use a relay to avoid burning out the siren output on the alarm module. I have my horn and 15 sirens hooked up to mine. Nine in the front and six in the back. I also have two piezos inside. It screams. You can't make mine go off without being noticed