I think it is virtually impossible from what I have figured to eliminate it. It can be quite annoying if you are trying to operate while charging. You can shut off the controller though and eliminate the interference. What I would recommend, seeing as you have time is something like the Morningstar PS-30-M PWM controller. You will not have any problems with something like that.
Don't get me wrong on the mppt controller, I do have one, that's how I know. Mine is a Morningstar MPPT-45, it's very nice, but even interferes with the Ham in my truck when in close proximity, so will other peoples solar installations, lucky for you it shouldn't be a problem where you are heading.
That sounds like a fun fun trip. I'm sure various folks from the board will meet you along the way. Fun stuff. I haven't heard of that web site before, you might mention it elsewhere as well, nice stuff.
http:/graveltravel.ca