First off I would upgrade the factory alternator wiring. Just hook a heavy gauge wire from the B+ post on the alternator and run that strait to the "+" terminal on the battery. This by passes the undersized factory wiring and stock alternator gauge. Install an after market volt gauge in the van so you can keep an eye on the voltage level when parked.
Second I would install at least a 2nd battery(deepcycle marine) with a battery isolator. If your going to put them inside the van and not under the hood make sure you install them in a sealed and outside vented battery box. Batteries give off explosive gases and thats not something you want in your van.
Third, make sure you size your inverters correctly. They are most efficient near their rated capacity. Running a 200watt load on a 5K watt inverter is a total waste because most of the power is going to be used powering the electronics inside the inverter. Only buy inverters you can find the efficiency charts for. You may be better off running a few smaller ones that you could switch on as power is needed rather then running one big 5,000 watt inverter just to run a playstation and small TV.
And fuses.. Fuses everywhere. Would suck to have your ride go up in flames.