Setting up shipping for each product

I am new to this so please ignore my incompetence. I set up my USPS shipping extension with USPS and got a username. Once I set up my username I wanted to run through a test item in my store to make sure the checkout process is correct before making my site live. In the extension I set up all the different methods of shipping I use with USPS. When I went to checkout all the shipping methods I use show up.

For example the flat rate envelope shows up but what if I have a large product and cannot be shipped in the envelope. Is there a way, maybe in the product set up, where I can select certain shipping for each item? I will also be using UPS for faster services once I get set up with them.

I havent tested this yet , but when you list your item, in the data section you can put the items dimensions. I would assume, if that information was filled out it would then weed out flat rate envelopes, small flat rate boxes etc from shipping options if it were too big........... hmmm... I might have to have a play later and see if I know what I'm talking about lol

Product dimensions are not calculated in the USPS extension. If you want to simulate flat rate box rates, you can follow my tutorial on using Volume-Based Shipping here:

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

Check out this generic shipping module. Will surely serve your purpose.