The vibrational predissociation of Cl(2)(B)-He(2) has been studied using a full dimensional wave packet method. The aim is to investigate the effect of increasing the grid size in the dissociative coordinates and the propagation time, on the convergence of observable magnitudes like predissociation lifetimes and Cl(2) product vibrational and rotational distributions. In particular, convergence of vibrational distributions is significantly affected by an artifact caused by the use of finite grids and absorbing conditions for the wave packet, combined with the presence of a sequential dissociation process. The results show that the lifetimes and the Cl(2)(B) rotational distributions are not greatly affected by increasing propagation time and grid size. However, convergence of the Cl(2) vibrational distribution is very slow, and the strategy of converging this property by increasing the grid size becomes impractical. An approximate model to estimate the Cl(2) vibrational populations is suggested, which is found to provide realistic distributions as compared with the available experimental ones. The main feature of the model is that its assumptions are closely based on the nature of the vibrational predissociation process occurring in the type of complexes. This feature of the model, in addition to its simplicity of implementation and negligible extra computational cost, contributes to the general applicability of the approach to BC(B)-Rg(2) complexes.