Many public places have AEDs, libraries, malls, federal parks, etc.
You, (or the patient)should discuss this issue with their cardiologist. Controlled A-fib is quite common. AEDs are to stop arrhythmias that evolve from the ventricle. If the patient was at risk for ventricular fibrillation, the doctor might consider an internal defibrillator. Possibly, of more concern to you might be the common blood thinners used to control A-fib, as they might contribute to prolonged bleeding.
If you are still concerned about this, confine camping to populated areas, where an AED may be readily available.