Is there anyway I could run this particular extension outside the sandbox?
all my saved sessions go away once sandbox contents are deleted.

If you mean: run Firefox sandboxed except for that extension, then no.

Why not just allow session information to be saved outside of the sandbox?
There's a setting at:
Sandbox Settings > Applications > Web Browser > Firefox
to allow session management information to be saved.

Just be sure that your Firefox Options say "Show my windows and tabs from last time", and (not so obviously) don't allow Privacy tab > "Clear history when Firefox closes" > Settings, to delete the "Browsing History".

Sorry it's actually chrome

There seem to be two Session Manager extensions, so I'm not sure which one you use:
Session Manager (from tkaz.ec) <-- I tried this one. In my view, it needs a little work.
mghenlmbmjcpehccoangkdpagbcbkdpc

Session Manager (from tirokea)
bbcnbpafconjjigibnhbfmmgdbbkcjfi

You can probably allow direct access to the entire Chrome profile folder, or some checking might find out exactly which files need to be saved out of the sandbox if you state which one you use.

from tirokea<<<<<<<<

In some ways this is the better of the two.
I couldn't see how to modify the tabs that are in a saved sessions with this one, but I definitely had an easier time saving permanent (as opposed to temporary) sessions.

It appears that the only file that needs to be saved outside of the sandbox is the extension's file in the Local Storage folder:
chrome-extension_bbcnbpafconjjigibnhbfmmgdbbkcjfi_0.localstorage

There are several choices:
1) You could just allow this one file to be saved outside of the sandbox:
Sandbox Settings > Resource Access > File Access > Direct Access
"Add Program" button: chrome.exe
"Add" button: Navigate to and select the above file in the "...\Google\Chrome\User Data\Default\Local Storage" folder.
OK your way out.

2) You could use a wild card path to the file, and enter just the folder/file name:
Sandbox Settings > Resource Access > File Access > Direct Access
"Add Program" button: chrome.exe
"Edit/Add" button: *\Local Storage\chrome-extension_bbcnbpafconjjigibnhbfmmgdbbkcjfi_0.localstorage
OK your way out.

3) As a result of trying-out both extensions, it appears to me that allowing chrome.exe to have Direct Access to the entire "Local Storage" folder might be advantageous.
If other extensions also save their information in the Local Storage folder, then setting that folder in a Direct Access setting could make saving data from other extensions more successful, when sandboxed:
Sandbox Settings > Resource Access > File Access > Direct Access
"Add Program" button: chrome.exe
Either:
"Add" button: Navigate to and select the "Local Storage" folder in the unsandboxed Chrome profile
OK
Or,
"Edit/Add" button: *\Local Storage\*
OK
----
You may also be interested in a setting to allow Chrome to save words into it's custom dictionary file:
(none of Sandboxie's templates include this, including the template for direct access to the entire profile folder)
Sandbox Settings > Resource Access > File Access > Direct Access
"Add Program" button: chrome.exe
"Edit/Add" button: *\custom dictionary.txt
OK
(Obviously, this uses a wild card path, so it will work regardless of the actual path to the "Custom Dictionary.txt" file)

Awesome, #1 worked perfectly...now how do I undo it if I ever want to?
I tried but it won't let me....do I just remove the local storage directory?

Won't let you?
All you have to do is go to:
Sandbox Settings > Resource Access > File Access > Direct Access
Choose "chrome.exe" from the pull-down box, if it isn't already shown there.
Then select the item:
...\Google\Chrome\User Data\Default\Local Storage\chrome-extension_bbcnbpafconjjigibnhbfmmgdbbkcjfi_0.localstorage
(however it may appear in the listing), and then click on the "Remove" button.
OK

Ahhh ok, thanks
Now this shouldn't effect sbie's security much should it?

Not at all. There's no way for any program except chrome.exe to make use of the setting, and even then, chrome.exe can only write to the local storage file with that exact name.

You've been very helpful and I appreciate it alot!