I installed a remote start on a 99 SLK manual trans. It's not exactly easy to do but not impossible. I've seen wiring diagrams that make it harder than it needs to be - for example, wiring up to the parking lights directly rather than to the relay that activates them. I came up with a number of shortcuts like this. I was able to use the flat key on the SLK for the bypass which is less expensive than the fob. Too bad it appears difficult r impossible to get for a Crossfire.

Documentation here: SLK Remote Start

Even if you have an installer do it, printout the schematic and give it to them.