Oh, here's something else I just thought of... .
If you're going to be carrying low-sitting sports cars... find out how tall the fender box height is inside the trailer. My lowered Camaro's door height is 8" from floor to bottom of the door.
When I got my trailer, I ordered 4" drop axles. This elevated the deck height 4". I did it actually for ground clearance reasons, since the trailer hauls quads more than it hauls cars, and I often times end up offroad.
The upshot is that the fender boxes were reduced 4" in height, from 9" to 5".
The downside is that the rear ramp is at a steeper angle, so lowered cars might rub. Fortunately mine doesn't.
BUT... if you get the 6" extra roof height also, your ramp door will be 6" longer and that will ease that ramp door angle.
Next... axles. I got the 5200# axles on mine. This is plenty if you're just carrying around cars, SUVs and maybe some stuff along with them. I have a max cargo weight of 6400 lbs.
I wish I had gotten the 7000# axles. This would have raised the fender box height by 2", which wouldn't have affected my Camaro. But it would have increased the GVWR to 14k, giving me a cargo weight of almost 10k lbs. Why? Here's why...
When I got this trailer, I was planning to install a pair of 50 gal tanks underneath, between the frame rails. One would be for freshwater, the other for gasoline. I was going to install 12v pumps for each, and the freshwater would be to supplement the small 39 gal water capacity of my Lance camper. The gas would be to ease the filling up of my quads (no more lugging around 5 gal jugs).
Well, when I did the math and worked out the weight of the tanks, the weight of the water and fuel, and the weight of everything else that I wanted to carry, I exceeded the trailer's GVWR and also the tire ratings (the tires are good for 10,160 lbs at max inflation pressure).
So you're going, what in the H--L do you want to carry? Here's what I'd had in mind. My Grand Cherokee, which is 4500 lbs (yes, I've weighed it). Then in front of it, two 800 lb. utility quads. Then probably 500 lbs of misc cargo. Then the weight of the water, tanks, etc. It'd all fit. Barely.
So when I realized that wasn't practical, I scuttled the idea and have instead listed the trailer for sale. I'll continue to use it until I sell it for what it's worth (it's still useful, just not as useful as I'd wanted), and later on pick up a trailer with the right options. It was a valuable learning experience though.
I figure I have about $7200 invested in the trailer with tax, the material cost to finish the interior (I painted it and bedliner'd the floor). Since these things hold their value well, I shouldn't take too much of a hit on it when I sell it. But I figure the new one I want will cost about $1000 more than that with the extra options I need.
So again, the moral of the story is to be absolutely certain you've considered every possibility before you order.
Rob