I'm thinking about getting an open trailer for general hobby use
(hauling steel tubes, dimensional lumber, an occasional machine, and
an occasional car). I'm thinking tandem axle, electric brakes on both
axles, 18' long, and 7000 to 10000 pound GVWR. I've seen many of
these with a slanted dovetail on the rear-most 4 feet. I understand
this dovetail combined with 2 short length ramps make it easier to
load a low clearance vehicle. But I don't understand why a flat bed
and 2 long ramps wouldn't do the same job. Do long ramps bend
easily? Are they uneconomical in terms of cost and weight compared to
a dovetail? While they might be good for loading a car, I don't see
them helping if I'm carrying long tubes or wood.

Also, I've considered an enclosed trailer but have yet to see any with
strong tie-downs that would be appropriate for tying down a machine.
And they sure are expensive.
Although I don't have any names or links for you, I *have* seen
hinged, beavertail trailers where the beavertail is raised up level
with the trailer bed (I believe hydraulically) for normal
transportation. Lowered for loading cars, etc., but left up for
"flat" loads. The hinged beavertail seems to be a good design
improvement where you can meet both demands.
Ken.