Thanks everyone for the comments. Here are some answers to the questions that I have seen posted here so far:
Gas Cans (out front): Our Sportsmobile came equipped with a 46 gallon fuel tank (which gives us ~500 mile ‘safe’ range). When planning our trip, I noticed that it was about 260 miles from Coldfoot to Deadhorse. Coldfoot represented the last guaranteed chance to purchase ultra low sulfur diesel. ULSD may - or - may not be available in Deadhorse depending on various circumstances. My van’s engine will run on ultra low sulfur diesel - or - low sulfur diesel (1-D or 2-D)… but ULSD is what is recommended. I also have a diesel generator and diesel heater and did not cross check what types of diesel they ‘could’ run (beyond ULSD). As a round trip from Coldfoot to Deadhorse and then back to Coldfoot exceeded 500 miles (which killed any safety margin or additional exploring miles I had in mind), I just played it safe and went about adding an additional 15 gallons of diesel capacity. Now where to put it? After a few days of trying every location but the front, I decided that all of my other proposed locations had just as many drawbacks to running the cans out front. To off-set the added risk of having these out front, my plan was to not deploy the cans out front until after I actually left Coldfoot and was on the way north to Deadhorse. This whole apparatus was only intended to be used to go the 260 or so miles from Coldfoot to Deadhorse (nowhere else). When we started our trip, my home built fuel can holder + empty cans was mounted on the roof. The problem with that solution was that when we were camping for the evening and our roof was raised, any moderate amount of side wind would cause this raised top to flex/sway more than I was comfortable with. After only one night of having the top sway side to side, I decided to deploy my ‘empty’ fuel package our front early (in order to save the roof). As the cans were empty anyway, this amounted to little more than additional crush zone in a front end collision. I followed my plan of only filling these cans in Coldfoot and then driving to Deadhorse. Once reaching Deadhorse, I emptied the contents of these cans back into the van - which gave me my added safety margin back again (regardless of what was available in Deadhorse). Even though these cans remained out front for the remainder of our trip… the cans were all totally empty. As for the color of the cans… I wanted to paint them yellow (standard color for diesel containers) - but I simply ran out of time. The best I could do with the time I had remaining was to mark the tops of the cans with the word DIESEL and safety wire the screw on tops to the body of each respective can.
Having a 4x4 SMB vrs 2x4 SMB: The vast majority of our trip (main roads) could have been done without 4x4. There was a handful of places we used four wheel drive and there were another handful or so places where we use the clearance provided by the 4x4 package (without using four wheel drive). A two wheel drive rig that had like new tires with an open block tread design (recommend ‘E’ rating for a SMB), would do just fine on most of our route.
Fuel Mileage: Will post this in the next day or so, once I unpack my receipts.
Secondary Rear Tire: This was mounted to the rear hitch receiver via some custom mods I made to my MotoJackRack.
Rear Box: This is where I carry my tools, recovery lines, bottle jack, air lines, spare oil, Dremmel kit, camping chair, wood blocks, tow straps, bungee chords, fuel siphon, etc.
Recovery Equip. & Spares: Fortunately, we did not have to use any of this equipment on this trip. I did manage to get stuck once, but a pair of fuel trucks justed happened by and they gave me cover plus a tug to get me out of that jam.