Sold our travel trailer via consignment this year. My experience:
Tried the word of mouth private sale approach first. Two buyers wanted us to give it away, the third, when given the trailer specifications, determined his TV wouldn't be able to tow it.
Called the dealer we bought it from 6 years ago. Was told on the phone they currently weren't accepting units for consignment sale. Went to the dealer in person and spoke to the sales manager, we came to an agreement and 'net to us' price. BTW, the dealer apparently bases their offer on current wholesale price. The sales manager told me we would be charged a $500 detailing fee, plus any needed repairs their inspection may find (there were none). The manager stated the unit would be marketed on RV Trader and their own website. Brought the trailer to the dealer that weekend. It never even made it to marketing stage, it sold in less than a week, we received a check for the net proceeds two weeks later (they are a multi-state/store operation).
I would say if the trailer is free and clear, that works to your advantage. First question I was asked was did we owe on it. I did not sign any title transfer documents until the trailer was a confirmed sale (Florida has electronic titles now anyway).
If possible, try the dealer you purchased the trailer from first. I found it interesting I was told no on the phone, but when I went to the dealer and showed them the original sales documents, no became yes.
Might we have made more via private sale? Possibly. But I saw a number of trailers for sale (our exact year and model) that had been languishing on RV Trader for months. We hadn't used the trailer in 3 years, it was costing us over $300/mo in storage and insurance; we wanted it gone and were free of the aggravation of attempting a private sale and the potential scamming that goes with such a sale. So, our experience was positive. IT got even better when we sold our no longer needed 13 year old TV to Carmax for $14K the following week. I had individuals approach me over the last two years offering to buy the truck for substantially less than Carmax offered; so that worked out well too.
Good luck.