Update....been doing some more homework. Still thinking of replacing the stock tank in the spring.
Titan Fuel tanks -
http://www.titanfueltanks.com/GMC_Chevy_Fuel_Tank.htm62 Gallon extra heavy duty cross-linked polyethylene fuel tank. (234litres) (also can purchase an off-road skid plate to help protect the fuel tank).
Pros - larger tank, apparently does not extend below frame, lighter - thus less cost to ship to Canada
Cons - more expensive, as much as 25%
Full tank of fuel = 451 lbs
TransferFlow -
http://www.transferflow.com/gm_tanks_0.html56 gallons, aluminized steel (211litres)
Pros - less expensive
Cons - smaller, more expensive to ship
Full tank of fuel = 406 lbs
I would perfer to go with the Titan, but it will cost 300-400 more. And if I get the off-road skid plate with it, another 100 more. The additional weight of fuel I'm not too concerned about. Assuming my future 5th wheel has a pin weight of 2000lbs, still lots of weight room.
Oh what to do....