As others have said:
1. GN converter on virtually all mainstream FWs will void the frame warranty...PERIOD.
2. 18k GVW FW is solidly in dually territory. It's not what you can TOW, it's what you can CARRY. Figure that that 18k FW will have a =minimum= of 20%, or 3600 lbs on the pin, which is payload directly in the truck bed. Some FWs have upwards of 25% on the pin, so now you're north of 4k lbs on the pin. That payload doesn't include the hitch, people, tools and whatever other "stuff" you want to carry in the truck.
3. A long bed truck will usually have slightly more payload than a short bed and will give you more room in the bed for storage. As others have said, turbulence in the bed can be ferocious, so you need to only put heavy stuff there or use low-profile boxes. There are a lot of options for storage, though.
4. While a Reese Goosebox is an option, again, not all mfrs will warrant the frame when using one. Some do.
5. There are 3 main options for FW hitches. a) Newer trucks have OEM FW hitch prep. Several companies make drop-in FW hitches using them, B&W being, arguably, the premier hitch. Andersen makes a hitch that would use an adapter to use the OEM mounts. B&W makes the TurnoverBall GN hitch and the Companion FW hitch. Andersen makes a version of their hitch that uses the GN ball as a hold-down (doesn't have to be a B&W TO Ball). My biggest issue with the Andersen is that I'm not sure how well it would stand up to the weight of your FW, though it's rated to. All these options give you a clean bed when the hitch is removed.
Lyle
