Many thanks for all the helpful feedback. Roger described the space perfectly. The truck does have regen, so everything needs to shifted slightly aft. The dimensions of the genny are 22.75L x 17.3W x 20H, so I still think mounting it behind the flip-out fairing is doable with the front of the genny facing out. For now, I'm going to move forward with the gas unit and will look at diesel options down the road.
Here is a pic of the external tank configuration I'm considering. If mounted above the genny, it appears to be a simple gravity feed system without the need for a pump.
Here are rubber mounts that are also available which could help with the vibration issue.
In regards to the electrical aspect, what pitfalls do I need to avoid? As I said, I'm not going to be doing the work myself, but want to be able to better understand the specifics of what needs to be done in order for the genny to power most of the items inside the cab.
Thanks again, gentlemen. Your assistance is invaluable.