Figured Id throw in my two cents that I havent seen discussed:
A serious pro to the wood deck is that its low maintenance. Meaning when the wood warps, it gets stained etc, toss it and put new PT lumber down. Easy.
I had a 16' open before I went to an enclosed, but Ive towed my car with an 18' open as well. You dont think those 2' make a huge difference, but they do. A few other things I think you should pay attention to is how the beavertail is constructed in the rear. On my 16', I constantly drug mine because of the way the frame rail hung. Look at the different pictures vision.dynamix posted of the trailers. The one with the rally car is pretty clean underneath, whereas the open has a support for the beavertail that hangs down another 2-3".
Tongue length is important too. Most trailers are 4'. The 18' open I borrowed was 5 feet. It was a major point in why that trailer towed better. Also consider, I couldnt open the tailgate of my truck with the 16', but I could with the 18'. Another plus for the extra tongue length. Those Appalachian trailers with the extra 2" on the tongue? Nooooooooooooooooooope.
For those with really short strap lengths, consider some of these:
My straps in the rear are really short in my enclosed because of the D-Ring placement. The reducers got the ratchet out from under the car. 100% easier hookup.
Of course, all of this is moot once you decide you want an enclosed.
I will also submit, any time you stop anywhere, check your stuff. And I really mean check, not just a casual glance over. I had someone loosen my straps in Semora after leaving VIR. If any of you know how 57 is over Hyco Lake, there is no doubt the car would have separated from the trailer had I not caught this.