Biggest issue with a GN trailer and a 1/2 ton is weight. A good modern 1/2 ton of any brand can pull right around 9,500# to 10,500# give or take a few.
A 20' GN weighs in the 4,500# area leaving 5,000# to 6,000# for payload. With such a low payload you could not get a 25HP tractor, FEL, and 5' BH on the trailer with out being overweight.
A 20' BP weighs in around 2,750# leaving a payload of 6,750# to 7,750#. Much more reasonable for a 1/2 ton truck.
If you want to do heavy towing get a 1 ton and skip the 1/2 and 3/4 ton trucks. Now you can use a GN and have a real load on it. To me the 1/2 ton has its place and I own one. They give a good ride and can haul upto 10,000# occasionally. The 3/4 tons really should not be made in my opinion, again I have one. They should just skip the 3/4 and go strait to the 1 ton SRW. Again I own one and its hands down more truck than the 3/4.
Chris