A gooseneck with as low a deck as you can get and still get the truck on there.
For long trips you don't want to be pushing any more wind than you have to, so a lower profile is better.
Don't order a trailer that weighs (empty weight) much more than needed, but don't skimp on it either, get good strong axles and great brakes.
Take a look at a tilt deck trailer, works similar to a rollback for loading.. When I'm ready for a gooseneck trailer I'll look pretty hard at one of those.
For the weight of your truck I don't think you can legally use a tag-along trailer. Think 10,000 lb is all you can do without jumping through some hoops.
Grigg
