as was said above, you don’t need to worry about a “chassis ground”.
I would suggest buying one of these:
it may be a little overkill, but it’s what I used.
it has a connection at the bottom to which to connect the positive post of your battery. then you use blade fuses to distribute power to whatever you are installing–LED lights, USB outlets, 12V power outlets, etc.
it has a connection at the top to which you connect the negative post of your battery, and then there are terminals to attach the negative lead to whatever you are installing. (this is equivalent to the negative “bus bar” mentioned in a previous post).
I used 16 gauge wires, which are capable of 10 amps. the only items that really need 10 amp capacity are the 12V cigarette lighter-style outlets, but using the same wire throughout simplifies things. you should be able to find 16 gauge speaker wire on amazon or at one of the big box stores.