Thoroughly read the instructions manual that come along with all of your purchased equipments, as it will eventually help you installing the components easily and perfectly. In addition, manuals will also help you connecting all the apparatus safely.
Now pull the power, and ground it directly from the second battery.
After pulling power, solder all of the wire connections. Use stainless steel screws and silicone to mount all the equipment safely. Stainless steel and silicone is corrosion resistant, and it will last longer than usual.
Afterwards, mount the speakers directly to the wood deck of your boat. It is recommended that one uses an XTC baffle behind the speakers to provide the speakers proper air environment. Do not forget to put silicone on the speakers grill in order to secure their mounting.
Routing all wires cleanly will be a bit of a problem, but one must ensure that it is done perfectly. It is recommended that one put all the signal wires at one side of the boat and the power cables on the other side in order to have a clean routing of the wires. Tie together all the wires neatly by using a tie wrap, and put them under the panels with the help of C-clamps. Power it up, and your boat is now ready to rock.