Charging 2 batteries from vehicle alternator?

Quasar524

Looking to buy a motorhome for extended touring away from hookups.  Since a motorhome has two batteries that may both need to be charged simultaneously from the engine is a modified alternator normally fitted as part of the base vehicle conversion?  On boats with separate starting and service batteries it used to be not uncommon for either a second alternator to be fitted, or alternator pulley ratios revised to increase output.  This may not be possible in the confined space of a road vehicle engine bay, so how else to improve charging capablity?