For urban bases, I use Blick Artists' Modelling Paste. It's thicker than gesso and has a bit of texture. I presume there's something comparable outside the US.
If you lay it on thick it will crack a bit when drying. That's a feature for my basing. They can be filled in with a bit more paste if you don't want them.
I work small amounts at a time and mix in a bit of powdered RIT dye in varying colour recipes. Just have to get used to judiging hardening time, and it will harden quicker with the dye powder added. After it sets, I drybrush.