Here's a thread that should answer your question:
https://www.camaro6.com/forums/showthread.php?t=553224
In summary, a 16' will work, but 18 or 20 may be better since it allows a little more wiggle room to get the weight distribution right. Will also want to make sure the trailer isn't too narrow for the car.
As for enclosed vs. open trailer, as long as you don't mind your car being out in the open when it's loaded the open trailer is much more economic. Cheaper to buy up front and cheaper to tow. Open is also easier to load assuming the car doors clear the trailer fenders.
Enclosed trailers offer the benefit if being a little more useful all around. I've used mine to sleep in on multi-day track days and can offer some shelter if you get caught in any less-than-ideal weather. However, they cost more up front and are more costly/difficult to tow due to aero load. They're also more difficult to get in/out of without the side access door because the car doors can't be opened as far. This is especially an issue to consider with the Camaro since the doors are pretty long.