Simply testing volts, any inexpensive multi-meter, analog or digital, will work.
If the batteries are installed in camper, they are already tied together, no need to jump terminals between. Testing one battery will show average of both batteries. If there is no load/charge source being removed-then no need to wait. To test individual health obviously they'd need to be disconnected from each other, and waiting a bit to watch as they stabilize.
IF your disconnect positively disconnects from any parasitic load that will work instead of pulling cables for summer storage.
