Mini-Buss Bar Power Source

I'm making a 12 volt DC power source (buss bar) to be located in the engine compartment of my truck.  The buss bar (copper bar) will be installed inside of a waterproof junction box and connected to the truck's battery with 2/0 marine grade battery cable protected by a 300 amp circuit breaker.

I'm having problems with 2 parts of the design.  1) I can't find a waterproof, manual open/close, circuit breaker rated at 300 amps and  2) I want to drill and tap threaded holes into the 1/4" thick copper buss bar for connecting "add-on" smaller gauge wires (fused) that will deliver power to various things.  These smaller wires will be connected using a soldered wire terminal held in place by a "threaded bolt".  Now for my question .. what material can the bolt be made of ??  I would like to use stainless steel but don't know what effect will be caused by the two dissimilar matals, copper and S.S., working together.  Are brass bolts a better choice ??  Any feedback will be appreciated. Thanks in advance.     

"Menace ........"

Your right ... but I did not explain the full scope of the project.  Without making this a long post ... I will have 14 each, 3"X3"X1/4" buss bar "pads" that will be connected together by 2/0 gauge wire (3/8" bolts thru 2/0 terminals).  Eack pad will have a 2/0 gauge wire input from the previous pad and a 2/0 gauge wire output to the next pad.  Each buss bar "pad" will have 10 drilled and tapped holes to connect individual 14 to 20 gauge wires to feed add-on circuits.  Each "pad" needs to handle up to 300 amps as a pass through current plus have enough surface area and thickness to mount two each 3/8 diameter bolts plus ten each #10 bolts spaced so my thick fingers can work on them over and over again.

Sooooo .... I'm back to what material for the bolts ????          Regards.

there will not be any "effects" on using two different types of metals,    i found a 200 amp breaker.  im sure i can find one for you here in "spocompton" if you need me to.

"Menace ........"

Thanks for the feedback on the bolts ... I think I will use stainless steel bolts.  Also, the more I think about protecting the total system the more I leaning towards a Class "T" type fuse instead of a circuit breaker.  I have found a Cooper Bussmann 180 series circuit breaker with on/off switch feature P/N  185150F which is a 150 amp breaker, the largest they make in that series.  Getting back to the fuse ... I will mount the fuse in a waterproof junction box next to the battery.  If you think of anything better please post.  Thanks for your time and effort.