The difference between liners like Kreem and others from 10-20 years ago and todays liners are light-years apart. The new Caswell liner is a 2 part epoxy that you can put right over the rust, in fact it "actually prefers to bond to a rough rusty surface" as opposed to Kreem and the others that they want you go through several cleaning stages to keep it from failing. It's these cleaning steps that are the reason most often that the sealer fails due to not being done correctly or extensively.
Here's what Caswell says about their product:
Phenol Novolac Epoxies are a new breed of chemical resistant materials, able to withstand permanent immersion of many harsh solvents, fuels and oils. This Epoxy has much better bond strength than single component products, with strengths of up to 3000 PSI, and this higher strength reduces the need for a clinically clean surface, as the epoxy actually prefers to bond to a rough rusty surface. Our new phenol novolac is more thixotropic, which means it 'hangs' on the tank walls during the coating process. This gives a thicker overall coating. There is more volume of material in the kit to allow for this.
I agree, there is nothing pleasant above removing an old failed liner. if a customer brings me a tank to powder coat it gets handed right back to them until THEY have the liner removed.