We traded both truck and trailer to the dealer we bought our C from. I know we probably could have done a bit better selleing both individually and privately, but we just wanted a clean single transaction and we got what we wanted in trade value.
We use a storage lot for our class C (and did for our TT), so showing the TT and going out there all the time just didn't seem appealing. And dealing with people flaking out and no-showing and knowing who to trust to test drive the truck was just not my cup of tea. Plus, we were pretty sure the truck would sell before the trailer then we'd be stuck with something we couldn't use just sitting there unused and depreciating, waiting for a buyer while we tent camped since we didn't have another vehicle to tow the TT. It ended up being a good decision because the truck is long gone from the dealer's lot, but the TT is still there (though grossly overpriced.)
And the other thing is that we saved in sales tax since we're taxed on the net amount paid after the trade, which was the majority of the purchase price.