USPS Shipping Info / Custom Packages?

Any way to get USPS to configure properly with bigger packages?

Example: I sell a container that is 14" x 14" x 28" tall, so it's a bigger container. Only weighs 7lbs, so it's lightweight. On the store, I have FedEx and had USPS setup to work, but it lets you ship this Medium Flat Rate Box, which of course it won't fit into... any way to only let USPS for certain items or to make it know that the dims are too big for said box? The dims are set on the item description in the products panel...
Thanks in advance.

The built-in USPS extension does not utilize dimensions of products. You can try this free extension, although I've never used it so I don't know if it works:

http://www.opencart.com/index.php?route ... n_id=15602

If it doesn't work for you, and you want to set up flat rate boxes on your own, you can do so with my Volume-Based Shipping extension. I have a tutorial available on how you'd do that here:

http://forum.opencart.com/viewtopic.php?f=114&t=85148