Strongly coupled confining models with a first order phase transition present an interesting DM candidate. Near the critical temperature these models are strongly non-perturbative, and the critical bubble nucleation rate has so far only been estimated via approximative methods. As a model of a strong first order deconfinement transition, we simulate 4D SU(8) pure gauge model with multicanonical Monte Carlo. We demonstrate that resolving the critical bubble is possible in a strongly coupled model. We calculate the free energy of a critical bubble, which gives a rough upper limit for the nucleation rate. For the parameter points we investigated, the thin-wall approximation for the critial bubble free energy is off by a factor of 2, overestimating the rate at least by a factor of $e^{10}$.