Just a guess, but it sounds like you have a leak in the airlines to one of your the "3030can" that actuates the brake OR you have a internal tear in your brake diaphragm and I'm guessing the latter.
* What does your tank air pressure gauge(s) read? ...Does it change when your air brake problems appear?
===> This is the best advice I can give you if you are not a mechanic===>
My Hartford insurance will reimburse me for Emergency Roadside Assistance LABOR (only). So I recommend you call your insurance company tell/ask them: I need a mobile mechanic. I cannot drive my RV. And if I call a local Diesel Repair Shop to send a mobile mechanic, will you reimburse me for labor?
Just for grins, if you want to know how to service your 3030CAN you can watch this video:
Note: Repairing a "Can" is easier than replacing one, but if your insurance covers the labor then I would ask your mobile mechanic to bring 2 cans with him and replace them both!
...If your insurance does NOT cover labor, and if you are CAPABLE of doing this repair, then by all means do a "half-can" repair or just replace the rubber diaphragm inside you existing can.
And for all the rest of use, this sort of thing is something you need to be aware of when you are driving a 15+ year old RV, because the diaphragm can not be inspected from the outside. ...And then one day: "Boom" you are stuck. So it pays to have a backup plan or at least know what to do.
One might go so far as to say, it makes sense to carry at least 1 or 2 rubber diaphragms (for your 3030can) with you since they are so cheap.
Please keep us posted. And let us know why your air brakes failed?