We start with quasi-exactly solvable (QES) Hermitian (and hence real) as well as complex PT -invariant, double sinh-Gordon potential and show that even after adding perturbation terms, the resulting potentials, in both cases, are still QES potentials. Further, by using anti-isospectral transformations, we obtain Hermitian as well as PTinvariant complex QES periodic potentials. We study in detail the various properties of the corresponding Bender-Dunne polynomials.