Second alternators are nearly mandatory as a practical measure when the engine alternator charges at the rate of 40 amps, or even 80-90 amps as yours if you have lithium ion battery banks greater than 400ah or 800ah such as I have.
Do the math in how much driving you desire to do in a day. If you desire to stick to the popular 330 or drive 3.5 hours per day or stop at 3:30 PM 40 amps can replace only 140ah. Solar on a B can provide a smaller negligible percentage of recharging per day, you can't run an Onan generator long enough for all practical purposes (by CG regulation, location or how much you can stand the noise) to recharge a battery bank. You thus are tethered to shore power campgrounds thus negating the need for high amp lithium battery banks. Shore power limits you to where and when you can camp.
High amp battery banks allow you to use your B electrically everywhere such as boondocking in a Walmart parking lot as transparently as if you were plugged into shore power. Every 120a outlet is hot with an inverter turned on, you can use your microwave or convection oven all the time, my Keurig coffee pot is at the ready anywhere, anytime and makes two cups of coffee while taking the time needed filling up fuel at a service station or a rest stop break, large compressor refrigerators are the norm, electric induction cooktops and instant pots can be used freely. What the heck, I have articulating beds that convert to lazyboy loungers at the ready with a vibrator mode to relax after a long hike.
With the second alternator coupled with high amp battery banks, of course you tend to take advantage of your batteries and use them profligately with no need to conserve or monitor closely. Some can reach the holy grail of the luxury of boondocking with air conditioning. It frees you up in completely eliminating propane, Onan generators and solar panels on your roof. With a small B eliminating those items can free you up in weight and space for other things. The roof trends are more active use such as rooftop decks, more skylights, and toys like kayaks instead of a deck of solar panels needing unobstructed sunlight.
As long as you drive at least every three days as most Class B's do you can live like this all the time. I use my B almost every day anyway for driving to a trail head, touring, going some place or just stocking up at a store. Not being tethered frees you up.
Everyone talks about this. The engine idling aspects and fears are overblown and over sold. I just checked, in over 85,000 miles and four years of travel, I have 17.5 hours idling on my van (it's monitored) and I can guarantee you most of that is testing it or demonstrating the capability to others.
That is what I have had for 4 years in an extended body 24 ft. Sprinter. Now I want that same capability in a 144 WB five feet shorter Sprinter (19'-5") on a 2500 chassis. You can't achieve that capability without a second alternator and lithium ion batteries with a 2500 chassis.
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