Encrypting Amazon EC2 boot volumes via Packer

In order to layer on some easy data-at-rest security, I want to encrypt the boot volumes of my Amazon EC2 instances.  I also want to use the centos.org CentOS images but those are not encrypted.  How can I end up with an encrypted copy of those AMIs in the fewest steps?

In the past, I have used shell scripts and the AWS CLI to perform the boot volume encryption dance. The steps are basically:

1. Deploy an instance running the source AMI.
2. Create an image from that instance.
3. Copy the image and encrypt the copy.
4. Delete the unencrypted image.
5. Terminate the instance.
6. Add tags to new AMI.

The script has a need for a lot of VPC/subnet/security group preparation (which I guess could have been added to the script), and if there were errors during the execution then cleanup was very manual (more possible script work). The script is very flexible and meets my needs, but it is a codebase that needs expertise in order to maintain. And I have better things to do with my time.

A simpler solution is Packer.