I used a cheapo kit with:
A tray
2 hold down bolts
1 hold down strap
1 long red cable
1 short black cable
You have to bolt the tray to the rear frame rail.
Run the hold down bolts through the tray.
Put the strap on top of the battery, with the bolts going through it.
Mount the ground cable to the frame rail.
Run the red cable through the body up to the front.
If you take your door sills off, you can run the cable from the trunk and through the sills and out the front fender in one easy stretch.
The fact that everything is bolted down to the rear frame rail keeps everything secure in any situation.
You don't need a box as long as you have an actual trunk that is separated from the passenger compartment.
If you have a hatchback, fold down seats, removed back seat, or holes in the rear deck or seats... then you will need a box with road draft tube to control any stray fumes.
I had alot of trouble with grounds. I found that I had to reinstall some stock ground straps and that relocating the starter solenoid to the trunk helps things.
Good luck
Dave