for weight trolling, I suggest something with more backbone to pull the 2>4 oz you'll need to reach depth.
Fisherman's Marine in Delta Park Portland has the Berkley Buzz Ramsey series rods on sale. get the 8lb to 12lb or 8 to 14 lb rated Buzz Ramsey Berkley IM8 graphite casting trolling rod for weight trolling.
http://www.berkley-fishing.com/prod.php?k=310007&sk=266020&p=PURA92-10-6XH (1139437)
good steelhead and lt. salmon silver rod also.
still rig up the reel on it with 8lb test, plenty heavy for kokes and has stretch/give for the soft mouthed kokes.
the Lamiglass glass rod, the Team Kokanee Jared fiberglass along with the Diawa lt. rods won't handle weight trolling. by the time you get 3oz of weight, sling blade and lure you're up to 6oz or more. need backbone to pull that.
Yale Reservoir is just up the road and river from Merwin, really hot koke fishing this year and a natural heavy spawn lake. far less crowded boat launches on the weekends than Merwin zoo.
http://www.lewisriver.com/yale.html
Fisherman's also has hollow egg sinkers and mooching banana shaped sinkers for low resistance trolling. i like the hollow egg because they will slide up the line when a fish jumps, less chance of the fish using the weight as leverage to pull out hook.
use a 1/4" bead below the egg sinker on the line so the sinker doesn't damage the knot.