That's the same alarm as me and my dad are gonna fit to my car. Cost me £125 for the alarm. We won't have to get in behind the dash though, you can access most of the wires at the fuse panel under the steering wheel. There is a lot of extra wire on the car loom, so you can pull the wires through for access, then push them back. The connections will be then hidden behind the dash. We have already marked and found what wires go where etc and decided on our mounting points.
BTW, when I bought this alarm, I got a wiring instruction pamphlet with it for the 155. Connect green wire to blue wire on loom under hee haw etc. Looks fine and can find all the mentioned wires.
You can alter all the settings ie. do you really want the car doors to lock with the ignition on ???...what if you need to get out quickly after an accident etc.
It is a very good alarm by the way, I would recommend it.
Did you know that the alarm unit has a rechargable battery in it ??? Even if someone cuts wires or the car battery goes flat, the alarm will still work. Cool !!!