Certainly can't say how every coach is wired, but my small solar panel charges my chassis (engine starting) batteries in my 2003 Dutch Star. I have four additional panels to supply energy for the coach demand and to maintain the battery bank.
When on the road we seldom use enough battery power to require anything but limited use of the genset to run the AC or microwave or the coffee maker in the morning. All of those items draw pretty hard and suck the battery bank down quickly or in the case of the AC won't allow both roof top units to operate.
Our coach batteries recharge from the alternator while driving as well as the chassis battery.