Yeah, FeeBay is a hassle. I do have other vehicles I could use, but this one is just cool...lol To secure it, I would useI mean... if you know that you don't want to hassle with listing/ shipping it and assuming it wouldn't bring much money to do so, I might use it in the way that you're describing. If there's a chance that you might be able to get some kind of decent return and that you'd actually list and sell then I'd scrap the idea of using it. Also relative to this would be "What other vehicle do you have that you could fit onto that trailer?" If you don't have anything else that appeals to you or if you'd have to spend money on something then maybe just go with your idea.
On e thing that may be worth considering also, is how you plan on securing this ( or whatever other vehicle) to the trailer... assuming that you plan to actually use the trailer and that it's not simply going to be a static display. Some vehicles/ trailers are easier to work with than others regarding securing/ tying down and also how easily it will be to remove.
I recently built a 1/10 trailer that is to accommodate a TF2 as well as a Capra and there was a good deal of thought that went into being able to have it hold two very different vehicles as well as how easily they would be to swap out. In your case I'd guess that's not as much of an issue since the car isn't RC but just food for thought.
D-rings and true-to-scale chains. I'd mount a winch and everything. And yes, I plan on using the trailer at shows and get-togethers as that "Lil extra" flash for scale points.