A big improvement is the use of lunar descent module to store O2 and CO2 scrubbers. The base on BLU only had storage inside of modules with an atmosphere. This caused the O2 and CO2 to degrade. The lunar descent modules don't have an atmosphere and keep the O2 and CO2 tanks charged up.
The PUR base uses a habitation module for living space and a cargo bay for storage instead space station modules. These modules are shorter than a standard station module and reduce the risk of collisions when landing or taking off from the base.