Breadboard in veh?

Just wondering if it would hurt anything to have me a little project box and a breadboard all nice and soldered together inside a vehicle. I know there is heat / cold / humidity to deal with and I just curious if there are any major reasons why I shouldn't do this. Also do I need to be concerned about losing Ohms and such with an alarm system? Doesn't seem like I would with this but I want to know nonetheless.

Below is my diagram I made in Paint. My idea is using some screw terminals so all I do is cut some factory wires, put them into the screw terminals, and then I can play around with the power and such all I need on the breadboard then route it out other screw terminals to the alarm and radio and such. The main reason behind this being I want to get the job done fast and I want to keep all the little parts together and simplify it all too. The diodes in the diagram are to keep the signal from the GEM from setting off the alarm, which seems to be an issue on Fords. The relays are for doing the "Radio on until door open" thing that is in the relay section of this site.

So please let me know if this looks like it will work and / or if it is even a good idea to do in a vehicle.

Opps there should only be one output to the alarm for the door trigger, the diodes to isolate are not on the diagram but would be when I do this.

Not being able to edit my posts is annoying...