My Onan weighs almost 300 pounds. It was a PITA getting it in the compartment which is probably easier than getting it out. First, disconnect the battery at the battery end. There are two battery cables that you need to disconnect from the generator. (make sure you disconnect the battery end first or you will almost certainly short something out and you want to make absolutely sure it won't accidentally start when your crawling around on the generator.
There are 4- 3/8 hex head bolts that are tapped into the generator base that you remove from under the generator. The fuel line should be on with a hose clamp. Be sure to have something to plug the fuel line once it is disconnected from the fuel pump. . The remote wire harness needs to be disconnected. You also need to disconnect the exhaust pipe at the muffler. Finally, you need to disconnect the power output electrical wiring.
Unless you are built like Popeye, you'll need at least two strong guys with strong backs and some 2X boards to facilitate removal (which is only half the battle- you have to reinstall it when your done working on the landing gear
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Having installed my Onan, I would avoid removing it only as a last possible option. Everything involved in this is in a difficult to reach position.
Good, luck,
John