Should I insulate the duct trunk as I finish my basement?
All ducts are now required to be sealed (at the seams), but you don't normally insulate unless:

they pass through a cold/hot environment such as an attic or unheated crawl space
you have an extraordinarily long run and need to reduce heat loss along the way

If you have a typical home, don't bother. Exhaust temps should remain acceptable unless you're skirting the fringes of performance with an old or inadequate furnace. The key is to have enough vents for each room (based on square footage, windows, and other factors) and good return flow.
Use foil tape and/or silicone caulk to seal all joints and be happy.