Give us the payload of the truck (off the door jam) and a couple examples of the 1/2 ton towable 5th wheels that you are looking at.
Usually 1/2ton towable means, you have a max rated 1/2ton absolutely stripped of anything but the driver to stay within ratings.
Example: We used to have a relatively small 28ft 9000lb (GVWR) 5th wheel. Pin weight was 2050lb, 200lb for the hitch, 200-300 in misc stuff in the truck plus us....so about 2500lb total. Of course, we has a 3/4ton with 2700lb payload. Most 1/2 ton trucks don't have a 2500lb payload.