I'm putting this in effects, because you can run your bass signal through the modules with the Q118 module.
Unfortunately, due to $$$ issues, I need to sell off my Modular project before I really got it going. This was the beginnings of a 5U/MU modular system for bass. No trades here, I need the $$$. All modules just have a little bit of rack rash on the screw holes and are otherwise in great shape. Any discoloration you see if just due to dust (my studio is in the basement).
Synthesizers.com Box11 rack/power - This is a good box for 5U/MU modules, and it doesn't have to be only Synthesizers.com modules. Power harness is already integrated into the box, and you get power status LEDs as well as 2 x4 Multiples units that are built into the front panel. The included power supply is the Sythesizers.com QPS4, and it has enough juice to handle a good bit more than 11 standard modules. There is one decent size scratch on the back of the enclosure due to me being a damned clutz in the first moment I got it out of the box. It has seen less than 10 hours use and is otherwise in perfect shape. It was $230 new w/PS. I'll let it go for $160 shipped.
Q108 VCA - Pretty standard and totally solid VCA, you can never have too many VCAs. $80 Q107 SVF - Nice thick and huge sounding filter, with LP/BP/BS/HP modes, CV control of cutoff and resonance, 2 inputs and 4 outputs. $80 Q109 EG - nice and powerful envelope generator, plus two really standard mods that most DOTCOM users do to their EGs. The top switch changes the speed of the envelope response, the bottom one switches range between 0V/5V and -5V/+5V. $80 Q118 Instrument Interface - This is an awesome module, it has a very powerful 10x/100x/1000x amplifier in it, can bring any signal from line level down to guitar pickups or even a mic all the way up to a 5V signal to run through your modular. It also has envelope, gate and trigger outputs. Lets you run any instrument or mic through your modular system. $80