Given your smoking history I would really recommend subbing with synthetic urine. If you've got time you could pickup some test strips and test yourself at home. If you decide to go the subbing method just practice a little first to keep the temp within range. They usually do the physical frist and then allow you to dress and do the drug test. Keep the sample in your shorts till the physical. Then transfer it to a pocket for the physical with a heat pad wrapped around it. Then transfer it back to your crotch for the urine test.
Subbing really is the safest way to go for us serious smokers.lol It would take me a minimum of 2 months for me to get clean and I don't plan on getting clean just for a piss test.