We present experimental transport characteristics of long and ballistic superconductor - 2-dimensional electron gas - superconductor junctions obtained in a temperature range from 1K down to 10mK. Surprisingly the critical current I-c can be fitted to the ideal junction temperature dependence, I-c(T) proportional to exp(-T/T-0) approximate to exp(-L/xi(T)), with xi(T) the thermal coherence length, despite the presence of interface barriers and a to small I-c. We propose that the conflict between the experimental data and the theoretical predictions for these non ideal junctions might be resolved by employing concepts from the theory of disorder induced opening of tunnel channels.