a bus bar, just 2 copper bars, a pos and neg bar.
your batteries and anything that charges the batteries and anything that takes power is connected to the bars to evenly distribute the power,
checking the voltage drop is most important with solar systems so you dont loose power, when using shore or generator power a little drop is not that important,
usually no issue to have different charging devices connected all together, common to use several charge controllers on a single battery bank or bus bars,
a 400 watt solar system will give around 30 amps so is probably best to connect the controller to the batteries with a wire that can take 30 amps with a low loss,
panels to controller should be as short a distance as possible, controller to batteries should be short, batteries to inverter should be short,
8ga stranded copper, 4ft run, 12v system, 30amps max, should give less than 2% drop,
Voltage Drop Calculator
as a general rule a 100ah deep cycle battery can only take up to 10 amps of charging at a time without causing damage, a little less is better,
also a 100ah battery can only provide 10 amps of power, if it gives more it will drop below 12v and the device may stop operating,
true deep cycle batteries never provide a cca rating,