When I was looking around I found a few floor jacks that would get under vehicles 3 ½ or so, they are pretty expensive and I never got one but that might be what you are looking for? You might try Northern Tool or someplace like that?
I saw this jack a while back and had to check it out, I checked at several places and had one with-in a week! I found a place that offered free shipping for over $250, the jack was $1 above their free shipping cut-off so I bought it. I thought it was a great deal. Even with the lift it takes a while to jack one up to get the wheels off, this makes QUICK time getting a car onto jacks stands!
It works under the Rivs, pretty much all of them, and even though it is not rated for a lot of weight it will lift one end or the other of any of them, and my 72 is a pretty heavy car!
A couple of video links of it in action
It wouldnt be any help out on the road but in the garage its great!
I had previously gotten one like this from Northern Tool
It will get under the Rivs in several places, so it is some help. I had gotten this one before I found the bladder jack so havent used it as much since.
Good luck, there are lots of choices out there,