I'm also building a 2U DIY rack module out of my favorite little cheap pedals - putting a nice little bass/guitar preamp in there, from behringer pedals mostly. Why not? bdi, gdi, compressor, tuner, noise gate, and something to use for a cab sim probably. it'll sound great and will always be with me. Modelling on the fly, analog style, no amp needed.
It's lots of work though... and of course if any part dies I'll have to replace it, but I'm just mounting things front facing and routing is going to done internally using the existing 1/4" jacks. Yea, no foot switches yet, but eventually I could choose to control that too (doubt I'll bother though). Reason it's 2U is simply cuz I'm taking the control boards from each pedal and front mounting them, and it takes 2U to fit. Doesnt' directly help you I guess though being 2U, not to mention quite a DIY project....
Also, I'm in the process of throwing one of my old studio rack units into a portable rack ... I see no reason not to use something like this with the 1001rb bass head as well...
in my case a Digitech S200. it's a really really good, very cool digital multifx unit. I used it in my studio for many many years, but now I'm hoping to do more mobile stuff, and might as well use it on bass. Great modulations, other special effects, like truly crazy stuff.
https://www.guitarcenter.com/Digitech/S200-Multi-Effects-Processor.gc
You can grab things like that for less than $100 on craigslist all the time... and if they work properly still, they're a blast. On bass or anything else.