Dithering is the only answer here. Noise is a characteristic of the camera sensor, not the filter, so the filter isn't the issue. Try manually dithering if you can, even if it's just every half hour or so.
An auto-guiding solution that automates dithering would be best and "hands-off." In your case I'd recommend a additional investment of an ASIAIR which automates guiding and will allow you to dither in RA, which is probably good enough. The new ASIAIR Mini is releasing this month, so should pair nicely with a portable setup like yours. You also can get a small guide scope like the Arcturus Speedy Guide Scope (or something similar) and guide camera like the ASI 120MM mini. Whatever guide scope you choose you could probably jury-rig it to the accessory shoe of your DSLR, and should be stable enough for a wide focal length of 135mm.
Overall, eliminating walking noise by dithering will definitely add to the quality of your photos, which are already very good!
