SmartSend - If Total Cart Length/Width/Height >100

Hi,

I am using the SmartSend extension on OpenCart 1.5.6.4

catalogue/model/shipping/smartsend.php:
http://codepad.org/9fQHiNM2

The code above is unchanged, exactly as it comes in the extension.

I want to be able to calculate the total cart length, weight and height and if any of those values are > 100cm then I want this method to calculate the rates available.

I have tried using various pieces of code (because I am not skilled enough to write my own) from other extensions and default opencart php files to check if these values are >= 100cm, but to no avail.

Any help would be greatly appreciated.

Thanks,
CPC.