I got to watch the process at Road America, with two different trailers.
You're right--the approach angle has to be VERY flat to prevent the nose from scraping badly. Most trailers are designed very simply, with the back of the trailer folding down to form the ramp. That will never work for a GT40.
What Mike, Jack and Kirby did was to use some lengths of 2x12 to form additional ramps; one end was positioned about in the center of the trailer ramp, and the other end extended several feet behind the ramp--effectively creating a ramp for the ramp. Even that wasn't fully effective, and additional blocks of wood had to be strategically placed under the tires as the car was backed out of the trailer to raise the nose up sufficiently.
A long-term solution would be to construct permanent ramps which are hinged at the top, and mount to the inside of the trailer's ramp. In practice, the back of the trailer is opened, and blocks of wood etc. are placed under the bottom of the ramp to support it. Then the hinged ramps are unfolded (they are triangulated on the side for strength, and the side supports sit flat on the ground) and what you are left with is a ramp that is now effectively double the length of the stock ramp.
Provision for securing the ends of the folding ramps when the trailer is closed up is important--otherwise if you slam on the brakes while underway, the bottoms of the folding ramps will be carried forward by inertia and slam into the car--as a friend with such a setup found out the hard way. :furious:
I get to see all kinds of solutions like this in my job flying the C-5 Galaxy. The nose opens up, and the ramp drops down just like a car trailer. For many military vehicles, that is sufficient, but for certain low-profile things, a lot of creativity is called for.
Here's a photo showing just a couple of pieces of wood employed to ease the approach angle for an MH-60 Pave Hawk helicopter, which I flew from Iceland to Sierra Leone, Africa:
That shows the basic idea; for our purposes we'd need more, longer bits of wood.
Speaking of that, a couple of months ago, another crew from my squadron had to fly a massive gravel crushing machine (used in roadbuilding) to Afghanistan. That sucker was LONG, on tracks like a bulldozer, and in order to get it out of the airplane, they had to build ramps using layer after layer of 24-inch wide pieces of plywood. The two ramps were about 60-80 feet long or so, and they weighed 44,000 pounds!!!!! :shocked:
I'll post a photo of that deal if I can get one of the crewmembers to send it to me.
(Edit)
Boy, that took about two seconds--he was online. Here's the first photo:
And another one:
This is an extreme example of what's required in your case of course. Then again, the rock crusher weighed 130,000 pounds!