Back halfed frame and towing

[Vimes]

When you back-half a vehicle, or use 2x4 or tubular steel framing to build a frame, what effect does this have on using the vehicle for towing? And, is there anything that can be done to make it more able to tow? I've been looking at tow bars for my truck, and realized that if the shop doing my truck back-halfs it none of the tow bars made for it will fit anymore, and that got me to thinking about what would need to be done to get a trailer hitch.

My intent for towing is probably nothing more than 3000lbs, 4000lbs at the outside.