Not sure if your engine is in front of back. Either way I'd do the jacking under the frame of the coach, placing the jack close to a suspension mounting point. Please don't rely on the jack alone to support the weight while you're doing the repair. You should have some capable jack stands for support while you're doing the work. I've heard about some very sad stories of jacks failing while people were under vehicles working on them.
Another option and what I did once, is to use the leveling jacks to raise it enough to get the jack stands under it. Then release the levelers so the coach is resting on the stands.
The jack stands should be close to a suspension mounting point as well, since that area is designed to support all of the coaches weight.
I'm sure others will chime in as well.
Harley Ultra Classic (Geezer Glide) Rider, Retired US Army Paratrooper, fisherman, shooter. Proud to have served, proud of those that still do, or have done so with pride.
2005 National Dolphin 34'