In Kramer's photo below you can see where the Onan generator is bolted directly to the floor of the generator compartment. Compare that to the second picture of the Kohler generator in my old 310 is mounted to a separate tray and then the tray is bolted to the floor of the generator compartment.
I do know the later Onan generators are also mounted on a separate tray like the Kohler generator is as I have a 6.5 Onan Emerald on a tray and also a 4.0 Onan like Kramer's that is also on a tray.
Having a tray simplifies things somewhat but doesn't make the task insurmountable. The picture below shows the 310 with the generator removed from the compartment.
This last picture shows how I used 4 pieces of angle iron to mount the drawer slides. Overall it was actually pretty simple to build and install.
For Kramer's generator he would need to have a tray fabricated out of 1/8" steel plate. I've had a lot of trays fabricated similar to this and the cost isn't all that bad. Assuming you have decided to go ahead with the project the first thing would be to have a tray fabricated that the generator could be bolted to. You would then have to duplicate the openings in the the new tray to match the openings in the generator compartment floor, i.e exhaust pipe opening, etc.
As you can see in the last picture above 2 of the angle irons are mounted to the floor of the compartment and 2 are mounted to the generator tray. The drawer rails simply bolt between the two angle irons on each side.
Also in the last picture above you'll see two spacers under the angle iron bolted to the floor. Those were required because I miss calculated when I drilled the holes for the drawer slides and the tray was to close and wouldn't slide properly
The black angle iron is made from 1/4" x 1-1/2" or 2" angle and the angle iron bolted to the tray is 1/8" thick. I believe the tray angle iron was actually from some computer server rack frames.
The drawer slide installation raised the generator 1/2" higher than original. Still plenty of room left in the compartment. You do have to unbolt the exhaust system in order to slide the drawer open but I've not found that to be much of an issue. You would likely also have to lengthen the electrical cables and the fuel line.
On Kramer's coach it looks like the door hinges open so that would likely have to be addressed but I wouldn't think it would be difficult to come up with a way to mount the hinge.
Two lessons I learned while doing the 310 installation was to buy drawer slides that provide for full extension instead of 2/3 extension and to buy drawer slides with a locking mechanism so when you pull the generator out you can lock it in the open position.
All in all it's not an overly difficult project and having the ability to slide the generator out of the compartment is SO nice