I had similar questions here
. A few things I learned from that thread and other research:
1) The F150 with a Max Tow package and without the HD Payload package will probably be close to the Max GVWR, so you will not be able to put lots of stuff in the bed.
2) A WD hitch moves some of the weight off the truck axles onto the trailer axles (there are some scale sheets in that thread showing that)
3) According to the folks at Equalizer, a correctly setup hitch will transfer 50% to 60% of the tongue weight to the truck axles, the rest to the trailer axles.
4) You may also get close to the Max Rear GAWR.
5) You will probably be nowhere close to the GCVWR
In the end, we decided to go with a F150 Super Crew, 3.5L EcoBost, Short Bed with the Max Tow package to tow a 25FB with a tongue weight of 832 (unloaded).
To make that decision, we used these Ford Vehicle Specifications here
for the 2012 model to determine the towing and payload capacities.
The 2012 F-150
lists all the capacities like GAWRs and Base Curb Weights (plus all dimensions)
The 2012 Truck Payload Workbook
lets you estimate the curb weight with options you chose so you can estimate the GVW and the GAW for both axles, letting you calculate payload
The 2012 RV and Trailer Towing Guide
explains all the concepts like GVWR, GCVWR, and GAWR.
If you are interested, I can post the detailed numbers I came up with and how. But basically, we figure with 2 adults, 2 100-pound dogs, about 300 pounds of payload in the bed of the truck, a tongue weight of 832 pounds, and a WD hitch, we will be about
400 pounds below GVWR
300 pounds below GAWR-front
390 pounds below GAWR-rear
I stress that this is all an estimation
based on my understanding and interpretation of the information above. Your (or mine) actual results may vary! I will post the actual numbers once the truck and trailer are delivered (by April we hope).