Kreem is the bane of the Riders of Vision, the Yamaha XZ550R, which has a tank that WILL rust if steps are not taken to prevent it. The angular design leaves 4 pockets below the petcock where water can and will pool to rust it from the inside out.

The Suzuki GS tanks don't have this design, so should be safe without a liner, so long as fuel dryer is in the regular diet.
Water is heavier than fuel, is why the bottoms of most untreated tanks rust out. And, like the ROV, this forum involves folks that tend to hang onto motorcycles longer than the norm, is why Kreem shows degradation. POR-15 and Caswell are both better solutions, but you can get away without lining your tank, if you keep water out of the tank, as in treating the fuel with line drier and keeping the full tank when not riding it. An inline filter can go a long way to saving the parts downstream from the tank, too.
So, if you have a tank that isn't rusty, don't bother lining it, just apply line drier at least once every two weeks, install a filter, and end the rides with filling the tank. :-D
If, OTOH, your tank is rusty or leaking...then, think about lining it. :|
Personally, I've used Kreem in 3 three tanks, have 2 more that were lined from the factory. I've had the Kreem in those tanks for more than 15 years, and have seen none of the problems that most people cite. Butt, I was rather extreeeeem in the preparatory steps before I lined them. There was NO residual PHO or water in the tank when the liner was applied...the tanks sat for more than 24 hours with the PHO in them, or until the bubbles stopped forming, and dried for more than 36 hours after the acetone was used to remove any water. We'll have to wait to see if this treatment makes the Kreem stay put... [-o<