The talk of sleepers, benefits, etc. are all dependent upon you applying for, attending an interview for, and getting hired for a permanent position whether it be package handler, Package Car Driver, or Dedicated-customer CDL driver. I'm not too sure about how feeders works because I was not in feeders; whether or not they will post off the street full-time permanent openings for tractor-trailer drivers after peak season is what you will be depending on.
The only thing you're guaranteed is a seasonal job. Whatever was discussed was a carrot dangled over your head, should you reapply after peak season when you are let go; which will happen because you, as stated above, are a seasonal driver with no expectation of full time permanent status or any protections or schedule restrictions afforded to Teamster drivers. That comes after peak season usually with a separate interview and position that is specifically written to be permanent.
I could go on and start an irrelevant discussion about railroad terminology, if needed....