The analysis of processes occurring in non-standard environments like the atmospheres of exoplanets or the Earth troposphere requires accurate kinetic data at low to moderate temperatures and involving barrier heights spanning a large range of values. Furthermore, medium-to large-molecular systems are often involved in those processes, whose entrance channels are tuned by non-covalent interactions. As a consequence, reliable yet effective methods for the computation of rate constants and branching ratios are needed. The master equation formalism employing ab-initio transition state theory offers a reliable reference frame, provided that accurate structural and energetic parameters are available for the key stationary points. To this end, we have validated the recently proposed junChS-F12 model chemistry with reference to very accurate energetic and kinetic data. The results obtained for a large panel of systems and reaction channels show an average error well within chemical accuracy for all the key thermodynamic and kinetic contributions without the need of any empirical parameter. The junChS-F12 model delivers smaller errors with respect to the reference values than its conventional junChS predecessor, without any excessive increase of computational resources. This behaviour can be traced back to the strongly reduced role of CBS extrapolation when going from conventional to explicitly correlated composite methods, with the consequent reduced role of the errors incurred from its estimation by low-order perturbative methods. The computational bottleneck of the proposed model chemistry is the CCSD(T)-F12/jun-cc-pVTZ step. In this connection, new low-scaling approaches and, possibly, local-correlation models deserve further investigation in order to increase the dimension of molecular systems amenable to accurate computations with reasonable computer requirements. Additional refinements and validations are needed also for situations involving non negligible static correlation and/or non-adiabatic effects. However, even taking these limitations into account, we think that the strategy proposed in the present paper can contribute to the computational study of chemical processes under widely different temperature and pressure conditions.