My first iteration of the interior of my ATC Bobcat shell was an all electric camper, both 12 VDC and 110 VAC. No propane.
I used to carry my Honda i2000 on the front floor of the camper. I wanted the weight as far forward between the axles as possible. The Honda i2000, like many modern portable generators, have an ability to completely close the gas cap vent so that no gas fumes exit the gas tank. Pulled it out for use when camped.
If you decide to mount on the exterior for storage and use, there are some neat solutions to protect the generator (both from the elements and theft) and eliminate vibration, by hanging the base of the generator by rubber straps. You can probably find the video's on the internet, possibly on YouTube. It's been too long since I looked at them to remember exactly where they are located.
I have remodeled the interior of my ATC Bobcat shell to eliminate the 110 VAC and now have a propane tank, a propane flush mount glass top double burner stove, and a low amperage, 1.8 amps per hour, propane furnace. I'm nor going back to the 110 VAC, love the interior the way it is now.