Automated Configuration which includes persistece you can use the following utility but I have not tried it:
ecryptfs-setup-swap


Manual Configuration
This Configuration uses randomly generated keys at boot and will not support Hibernation to hard disk! You Should Disable Hibernation through your respectie DE Power Management Utility and set it to Shutdown on Critical to avoid Data Loss!

### Switch to an admin/root account
su root or sudo for each command

### Disable Swap
swapoff -a 

### Locate the existing Swap Partition
lsblk

example:
sda3                                          8:3    0     8G  0 part [SWAP]

### Overwrite Old Swap
dd if=/dev/zero bs=1024000 of=/dev/sda<#>

example:
dd if=/dev/zero bs=1024000 of=/dev/sda3

### FSTAB setup
vim /etc/fstab

Replace old SWAP device with crypttab mapper name: /dev/mapper/cswap

OLD
UUID=d03f3d8e-7888-48a5-b3cc-41de8dbbcfdc swap  swap    defaults        0 0

NEW
#<file system> 		<mount point> 	<type> 	<options> 	<dump> 	<pass>
/dev/mapper/cswap 	none 		swap 	pri=1,defaults	0 	0


### Crypto Setup

ls -lF /dev/disk/by-id

Example:
ata-HGST_HTS545050A7E680_TEK55D4F0BU3GV-part3 -> ../../sda3

vim /etc/crypttab
# <name> 	<device> 							<password> 	<options>
  cswap 	/dev/disk/by-id/ata-HGST_HTS545050A7E680_TEK55D4F0BU3GV-part3 	/dev/urandom 	swap,cipher=aes-cbc-essiv:sha256,size=256
  
### Active Encrypted Swap
Reboot The Computer 

### Verify Enctypted Swap Operations
dmsetup -C info 

Example:
cswap                                     253   0 L--w    2    1      0 CRYPT-PLAIN-cswap  

lsblk

Example
├─sda3                                          8:3    0     8G  0 part  
│ └─cswap                                     253:0    0     8G  0 crypt [SWAP]

cat /proc/swaps 

example:
Filename				Type		Size	Used	Priority
/dev/dm-0                               partition	8385532	0	-1