Severance agreement arrived, need a second opinion - 4 months and counting

I was offered 12 weeks of severance after 12 years as a welding apprentice, and I have a few days to sign. I have read a lot of threads here and could not find my exact situation. I do not want to leave money on the table. Did anyone negotiate and succeed?

Ask for the offer in writing and do not sign on the spot. A day or two to think is normal.