I have seen a couple items available for checking tongue weight. One item that I saw is the Sherline LM2000 that is a hydraulic scale that you place under the tongue to get the weight. It converts hydraulic pressure to weight. Pretty simple.
The other product I have been reading about it called Better Weigh. It plugs in to the truck obd port and, supposedly gives a read out of truck, trailer and tongue weight. I guess it works through the cruise control and trailer brake software on the truck.
Anyone know anything about these or similar products?