We installed the 51 gallon tank on our 2007.5 GMC 3500. It hasn't all been a bed of roses:
1. The installers (not an RV dealer) messed up re-installing the fuel sensor/pump unit, resulting in the gas gauge sticking;
2. They messed up the new vent hoses that are required, resulting in burping and a fuel leak. This despite the very detailed installation instructions, with photos, available for free from Titan's website;
3. The tank that we got was shipped prior to a recall, so the factory had to ship a revision kit;
4. The design of the tank seems not to accommodate the shape of the passenger cabin's floor at the front of the tank, so the tank's nose presses up against the pan, resulting in road vibration passing from the frame into the cabin, bypassing the cabin's rubberized mounting points (a flanking path, as the acousticians among us will recognize);
5. The tank holds about 370lbs. of fuel, split maybe 50/50 between front and rear axles on the driver's side only. The load on the front axle can sometimes slightly exceed the GAWR when we're loaded for travel and the TV will visibly tilt a bit to the driver's side (even without me in it
);
6. The shape of the tank, like a rowboat, causes the fuel gauge to hang at full for a long time, then rapidly drop as the pool of fuel in the bottom half of the tank shrinks - if we get to an indicated 1/4 of a tank, we start looking for fuel!
The installation and recall issues were solved by a return trip to the dealer and substantial amount of excellent support from the factory. We're stuck with the vibration issue, which I am considering how to amend. The weight and balance and gauge issues are ours forever.
On the upside, we can buy fuel at cheap places and drive by expensive places, grinning. Of course, it takes fuel to haul fuel, so we're only saving money if the difference is substantial. For example, the cost of fuel in Quebec is about 10 cents/litre (40 cents/gallon) more than in Ontario, so we fill up at the Flying J in Napanee, Ontario before driving to Montreal to visit our families and fill up again on the way home, saving $20. The tank we have is cross-linked polyethelene. If you go ahead with the Titan tank, make sure that: the dealer has done it before; the dealer gets their stock directly from Titan (not a third party that has old stock); that the tank will not touch the floor of the cabin; that your weight configuration can manage 370lbs (or the weight police will be bugging you
). I have pictures of the installation issues that I can send you if you email me.