I have a hydraulic bottle jack that I use for my motorhome. They're not always the most convenient to use, but they are relatively inexpensive and reliable and don't take up a huge amount of space. They do generally require comparatively much clearance underneath whatever is being jacked up, not a problem with the class C chassis.
Floor jacks (like DutchmenSport shows) are more convenient to use but not always the handiest to stow in an RV. Many are also relatively light duty, 3 ton capacity or so. I have one that I use for maintenance on my car, mostly rotating tires (in combination with a couple of jack stands, which allows raising all four wheels off the ground simultaneously and so avoids having to shuffle a jack around a lot in the process).
No jack should be relied on to support a vehicle while working underneath it. Proper jack stands or other safe, solid supports (e.g. well-constructed cribbing) are essential for that. For jack stands, check the load ratings with a bit of care; often the specification is per pair rather than individually.