Allan asked: (1) Battery tray recommendation: I've used Todd which have worked very well. Try a few camper/RV suppliers for price...or check online....I've seen lower prices at R/V than at good discount marine stores.. (2) Switch arrangement: No way to answer your question unless you first decide what it is you are trying to accomplish...then there may be several appropriate solutions. As you can tell from listoid's comments on batteries, TWL's have different (valid) ideas about battery arrangements based on how they use their boats and what equipment they have installed. (3) A shut off switch at main "house" battery is (ABYC) required to isolate it from all loads in an emergency...say a fire in your electric panel. Be sure cables can handle the highest current that will ever be required.....probably to start your main engine if other battery won't...West Marine Advisor has tables to help. When in doubt, always use a heaver rather than lighter cable. (4) It's easy to make cables yourself: buy appropriate size cable and heavy duty copper connectors from most amrine supply stores; just solder together,cool immediately in a cup of water and wrap exposed parts with multiple layers of electrical tape. (5) If you are not familiar with electrical circuits be prepared to be confused when you first confront them...Try West Marine Advisor as a start. As with the TWL list, different sources have different "correct" solutions. When completed, if you do it yourself, you'll have a new appreciation of this system aboard your boat. And you'll understand why the estimate/quote is so high. Be prepared for sore knees, a few (hopefully minor) cuts, some bruises..and as you suggestion, some satisfaction! good luck, Rob Brueckner