Just got back from a mini TAT (Utah and Colorado) and a full CDR trip. My intake/exhaust, etc. is bone stock. Twice I filled up the tank up, at the end of the day, and put in 3.7 gallons of gas (3.69 and 3.72 to be exact!). Ya, the 3.7 gallon Safari would have brought me in on fumes.....but I would have been stressing the entire day. Was really glad I had the 4.7 gallon IMS........worked like a champ
Nothing against Safari tanks....I have the 9 gallon fuel tanker on my DR650
. It's not a matter of brand, it's a matter of capacity.
For what it's worth, I'd either get the 4.7 gallon IMS....and never worry about fuel, or stick with your current setup and get a 2 gallon bladder from Justgastanks and rokstrap it to the back of your bike (full on the longer stretches and rolled/stowed on the shorter stretches).
Regarding weight... if the Rotopax is full (+ the weight of the Wolfman rack), it's probably going to weigh as much, if not more, than the 4.7 IMS when full... If it's not full, it seems like a lot of stuff to be lugging around without any purpose. If I was dead set on a Rotopax, I'd mount it to the tailrack (I know it sits higher....but it saves you from adding the bulk/weight of a Wolfman rack). Just my opinion.
FWIW, the toughest single/double track/no track!, I experienced on the trip, was in Black Dragon Wash....didn't even notice that the 4.7 gallon tank/fuel was there.
I think that this whole tank size/weight issue is a matter of perspective....If you're coming from a 650cc dual sport bike (which I was) or bigger, the WR with a 4.7 gallon tank seems really lightweight, small, and nimble..... If you're coming from a 250cc, full on dirt bike, and ride primarily single track, then the WR with a 4.7 gallon tank seems big, bulky, and heavy.
For me, I hate worrying about fuel....