Replacing bearings with Drylin bushings
According to igus commercial documentation, these bushings:


do not need any kind of lubrication,
are not susceptible to humidity (but your steel rods might) 
work seamlessly in presence of dust (it gets expelled from the bushing with movements)


I've replaced all of my bearings with these, and in my experience, the above claims have been true so far. I must say that I am really pleased with them. Movement is smoother, and the noise is considerably lower.

I did clean the rods to remove any trace of lubrication prior to installing them. I did not dry them.

I believe that igus is also selling rods in a material designed to even further improve the qualities of these bushings, but it starts to become quite an investment.