My experiences in that area are from the sports car racing side - not horses. In 2000, virtually no one built a car hauler with LQ. So, being the out-of-the-box kind'a guy I am, I designed and commissioned one. It was (is) built on a 39' wedge-nose convertible-hitch chassis (it is both a 5th wheel and a gooseneck).
The 5'er is easier to hook and unhook - and may be a little more stable on the road. The goose tows better on uneven ground and allows you to hook up where there is no way with the 5th wheel.
It is still alive and well (although unused, at the time) after almost 8 years. As far as what I designed in:
80G fresh water, 54G holding; Stainless sink, full bath with stand-alone shower;
Queen bed, leather dinette (converts to 36x74 bed).
Air conditioning w/heat strips; 6G water heater. Dual 30A shorelines.
34 gallons of fuel for the 6500W generator;
No LP - all electric; mini fridge, microwave, dual element hotplate, large toaster oven; TV / VCR /antenna;
It is a heavy duty rig - not a travel trailer with a box. Empty it weighs a bit under 12K, and loads out with the car at 17,500.
I went through 3 trucks finding something that would work (the orignal weight estimate by the builders was off by >3K#). We wound up with a F-550 PSD with an 11' Custom Carriage chassis. With the 7.3L and a wee bit o' help, it is an impressive tow. Loaded out, I can easily outrun my C7-powered Vectra in the hills - and getting 25% better fuel economy in the bargain.
Fully done with all the stuff we put on it, it wound up costing about $37K, in March of 2001.
Here's a few pics - if you wish to snoop:
Norm's race car trailer