Yes, I have installed strobes into several different vehicles. Personally, I prefer to run the cables underneath the step plates inside the vehicle. I've run plenty of wiring in my Expy, and there should be enough space for several cables.
I would not run the cables under the vehicle, because there is a much higher chance of things going wrong. It is also extremely easy to run wiring through the firewall into the vehicle.
I prefer to mount strobe packs and other equipment inside the vehicle as well. I have noticed that generation 2 Expeditions don't have a whole lot of room under the hood, and it would likely be difficult to find enough room to mount a strobe power supply.
Additionally, if you are planning on putting strobes into your headlights, you have to remember that the gen 2 Expeditions have two layers of plastic to get through in order to get the strobe through. You will have to drill a large enough hole to get the strobe through, and then the correct size to mount the strobe into position. The taillights should be much easier though, as they only have one layer to get through.
Be careful with hideaway strobes, as they do get hot, and you don't want them to melt the housing of the light that they are mounted in. You shouldn't have any trouble though, unless you want to place them into the reverse lights.