Small car battery VS Large Lawn and Garden battery VS Deep Cycle

I want to add a small radio and LED lighting to my open trailer. This will let me listen to track announcements, load up in the dark and not kill the truck battery. Also the battery for the trailer brakes needs to be replaced. So I am thinking a tongue mounted toolbox with the following:

-Retractable drop cord -Battery charger -Power strip -Boat head unit and speakers -Switches for lighting -All the tie-downs and trailer junk

Why are the Garden Tractor batteries so much cheaper than car batteries? Would a deep-cycle battery be smarter? Can I run the emergency breakaway system with one battery?

For your intended use, you need a deep cycle or marine style dual purpose battery. A car or lawn tractor battery will live a very short life if it's being drained and recharged. For an additional source of charging, you can take the +12v line in the 7 pin trailer connector (which should be good for 10 - 15 amps) and wire up one of these: http://www.xantrex.com/power-products/power-accessories/auxiliary-battery-charger.aspx

That would charge the trailer battery while you've got the tow rig running. Then you'd be partially recharged when you get home and wouldn't have to keep the trailer plugged in as long to top off the battery.

For the sake of redundancy, I'd tend to say keep the breakaway battery separate.

Either should work to cut up a canoe.

I would be putting in a lighter plug or 2 and a couple of USB plugs,

Plus a way to plug your trailer lights into the box if you towcar light plug dies or someone needs to move the trailer a short distance with tailights working......

Maybe a small solar panel to keep it charged ?