My 2 concerns with moving the battery to either trunk are:
#1 Acid spill in an enclosed area (Now you rot out the trunk floor
#2 H2 buildup in an enclosed space
There is a reason batteries have been left in "open" areas on the car. You don't want explosive gas buildup in an enclosed area. Solution? Battery cover and acid mat under the battery.
Oh and a sealed battery helps too!
James