London, are you climbing with rope backup? Before you consider napping in a tree you want to make sure you don't take an unexpected tumble, it would definitely ruin your day.

Try and stay away from putting anything "permanent" (like plywood) in the tree. The cool thing about a tree boat is that there's zero damage to the tree and nothing left behind when you leave. Go to New Tribe to see a description of their tree boat and other useful climbing equipment:
treeboat hammocks
-moss