By the way, if looking for hard data, these curves for optional 240-Amp extra heavy duty alternator from Ford for 6.2L V8 E-Series show that there is a wide range of capacity. On some motorhomes manufacturers specify the standard alternator, which may be as low as 120 Amps.
Higher-capacity alternators should make a greater difference when motorhome has multiple batteries. This alternator is rated at over 3,000 watts which could go into battery bank if large enough to take that much current. I'd sign up for that option for sure. The added cost is minimal.