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Tallarns would be a great base. Another alternative would be your basic Cadian with respirator heads and backpacks such as those from Victoria Lamb. These heads are great as they have a variety of faces, hair styles, and goggles.
http://victoriaminiatures.highwire.com/product/chem-mask-heads-x10

Combine them with these backpacks:
http://victoriaminiatures.highwire.com/product/5-chem-tank-backpacks

She has other various bits and detail pieces that could add a lot of character to your nomads.

Now use Ork trucks for the basis of your basic vehicles and if you want another light chassis, the Tauros venetor from Forge World along with some of the Ork truck variations.

I wish I could do some Necromunda/Ash Wastes, but sadly nobody in my area wants to.

Not sure, I am sure one could figure out a way though.