I think all the warnings not to use jacks at the axles are to prevent the uninitiated from placing a jack too far to the center of an axle, which can bend one. Think about it, the weight of the RV is centered over each spring perch. So, using a bottle jack directly under a spring perch is certainly okay. Most tire shops will use a rolling jack and put its pad directly under the spring perch. If I were taking off two wheels, I'd use two bottle jacks and two jackstands under the frame (as insurance) while the tires are being mounted.
--2005 F350 Superduty Crewcab, 6.0, 4wd, short bed, 3.73 gears
--2016 Montana 3711FL, 40'
--SOLD 2014 Wildcat 327CK, 38'