Instead of having both a Header and a Trailer Node, you can get by with only a single Header Node if you make the list be circular.

The last free block will have its next block be the Head "free" block.

The Head node will have its previous block be the last free block.

If the free list is empty, you still have a Head "free" node.

For an empty free list, the Head "free" node will have its hext and its prev equal to itself.