As someone who has begun to research upgrading my tow rig/trailer combination I have learned that in CA if the GCWR is over 26,000# then you need to have a Class B (non-CDL). Regular is a Class C. If you are going to tow a tag trailer or vehicle behind a 5th wheel (behind your truck) you need a doubles endorsement.

My understanding is that unless the vehicle is used for hire or is rated over 26,000# GCWR you don't need a CDL in CA.

Regarding placarding of HAZ-MAT, unless you are talking about certain POISON(s) or Explosives placcarding, and HAZMAT endorsements are not required unless the amount of that HAZ-MAT exceeds 500#. As long as you are talking about 1 drum of fuel and you aren't mixing it with other HAZ things you should not have an issue.