Well, those heavy tank destroyers were pretty much slabs of armour on tracks, with a gun projecting forwards. Although they're technically speaking assault guns and not tank destroyers, those crazy Sturmtigers are probably pretty much the reductio ad absurdum of the idea. I understand the Ferdinands initially suffered in the hands of Soviet infantry tank-hunters (Molotov coctails are mentioned with regularity in the list), and were soon fitted with MGs for close defense to rectify things (the resulting design apparently being known as Elephant).

Well, that one super-heavy tank the Brits got to a prototype stage - Tortoise or something like that - wasn't half bad in that regard either...