We present a formula for a generalisation of the Eulerian polynomial, namely the generating polynomial of the joint distribution of major index and descent statistic over the set of signed multiset permutations. It has a description in terms of the $h^*$-polynomial of a certain polytope. Moreover, we associate a family of polytopes to (generalised) Eulerian polynomials of types $\mathsf{A}$ and $\mathsf{B}$. Using this connection, properties of the generalised Eulerian numbers of types $\mathsf{A}$ and $\mathsf{B}$, such as palindromicity and unimodality, are reflected in certain properties of the associated polytope. We also present results on generalising the connection between descent polynomials and polytopes to coloured (multiset) permutations.