Are the house batteries charged? I think some if not most generators start from them. Also do you have a "boost" switch that allows you to jump start the truck from the house batteries? If so while the engine is running try pressing that switch. It should join all of them, then try the genny.
If the engine charges both house and chassis batteries then it may start by just running the engine. It depends on how the MH was built.
Mark & Nancy
2004 Winnebago Vectra 40KD
Shep dog, R.I.P. Kenzie dog Toad 2015 Jeep Wrangler Willys Wheeler