Summary: We discuss a simple example of an F-theory compactification on a Calabi-Yau fourfold where background fluxes, non-perturbative effects from Euclidean D3-instantons, and gauge dynamics on D7-branes allow us to fix all closed and open string moduli. We explicitly check that the known higher-order corrections to the potential, which we neglect in our leading approximation, only shift the results by a small amount. In our exploration of the model, we encounter interesting new phenomena, including examples of transitions where D7-branes absorb O3-planes, while changing topology to preserve the net D3 charge.