It's a slow day so here goes:
You've already done most of it very trick and thought out, so doubt any of this is news to you:
First plan for how to use for fun, and then think about for the worst case stuff.
Then think about how it all goes together. You're dropping 7-10K+ on this. Spend some serious time reviewing flexibility, weight, cost, usefulness, and frequency of need\use.
After it's been loaded for a month or two and you're happy with the configuration, go to the dealer and get it levelled. Check your weight on a road scale. That'll be the biggest effect on your range\economy.
Stop by some survey trucks and look at their cargo boxes and setups. They go a lot more "off-road" for work than most patch guys. Not lifted, no extra fuel\winch, and frequently alone in remote areas.
Fuel: Supertank or add 2nd tank underneath. Slip tank needs some kind of pump and may not work well with your cap\deck. Almost same range and most guys with those are filling up at rigs or farms anyways (some kind of discount). You may pay more now and then, but you don't have to worry about stabilizing fuel either.
Security:
Alarm system with remote start and ability to self-start by block temperature and maybe time. Additional cable to go to ATVs or other items on Deck\cab. Extends your securtiy zone a bit.
Use an obvious chain in addition to tie-down straps.
Cap\Deck:
Look at Diamondback (silver\black) or a ATV\Sled deck (Galvanized\black). Can haul ATVs and maybe enough stuff to a show so a trailer's PITA factor isn't needed. Decks slide in\out and have ramps. The racks make mounting points for lights, tiedowns and lots of other uses. A hoop frame and tarp on the deck hides everything and can give it that duece look. :>
Some decks have access door in front to get at head of box.
Drawer\cargo system:
Maybe a flat sliding drawer and make your own dividers. Most cargo boxes aren't that flexible for changing configurations, so look at some and make your own with metal dividiers.
Power\Lights:
Figure what you'd like for lightng and flexibility for it. Maybe also use it at shows/shoots to draw attention to your booth.
LED llighting in the bed is awesome. Three strips (sides and head). Also run a 12V cable with forklift or WARN connectors to power battery, winch, whatever from back. Charge things while you drive.
Power inverter hard-wired in with extension cords into bed and cab.
Switch to use "shore" power at events or hotel plug-ins. Plug extra source in same time as block heater.
Rigid lights and maybe flashing system using headlights as well (some work well with ballasts, some don't).
Lights that can light up deck and swing to side to light up sides when needed? Lights front\back, tied to hi beams?
Towing\recovery:
Not just you, but someone else who was even more unfortuate about getting stuck.
Double the straps you have now. Clevis's that fit through your bumper loops and more to tie straps and other vehicles together. Chains and hooks for same. Solid ground or good pull angles can be farther than you think. Untying straps is huga PITA.
Winch on receiver hitch setup for front\back. Why turn arond on highway to free someone if you don't have to? Not on lots of trucks and if you're stuck enough to worry about your winch connection breaking, you're past self-recovery. Can store in bed for better security and weight distribution. Keeps it easier to access than trying to dig out the end its on to move it elsewhere...
Upgrade your tires tread, but don't bother with lift kit.
Safety:
Cel booster. Tri-band type.
Bigger fire extinguisher than you think you need (20lb+).
Safety book showing closest hospital, RCMP and fire locations (can get free). STARS# and ERP visible for anyone in truck to read when rolled over?
GPS tracking has uses, some cons. Yes, over Onstar and phones.
Spot personal receiver. Can go not just where truck is. Can providing tracking and can send spot locations to set numbers not just something to emergency ppl. Pretty flexible and inexpensive.
Personal lightning detector? Cheap and has uses in outdoors.
