I think the useful thing to post here are sites with chronic transient issues; and chronic van and RV dwellers along with their plates.
The city itself has a map of transient complaints at
http://pdx.maps.arcgis.com/apps/TimeAware/index.html?appid=ac6a6abf1092482190984a5df9dfacb0

I believe part of the problems can be attributed to the needle exchange four blocks south, right inside the Menlo Park Plaza and the BottleDrop Center which draws both vagrant junkies AND dealers into the area. It has been said that MCHD don't follow the 1-for-1 protocol and would dispense syringes to people who do not bring any to exchange.