I use a changing bag and a Paterson Orbital. I've not had any dust problems, but then this part of NZ is not known for its dryness....

If you have a suitable 120 tank, you could use that to develop the 4x5 sheets - do a search on the "taco method". You can develop either one sheet slipped into the tank, emulsion side in, or multiple sheets if you use rubber bands around the sheets. Just make sure you have the centre column in on most plastic tanks to keep it light tight. This was the method I used till I got the Paterson Orbital.