I use 10&12# balls. Location, location, location. Mount one bracket left rear directly behind seat. mount one bracket right btwn. back bench & center bench. The seats are bolted to the gunnel which gives them rigidity. Aluminum is some damn tough material, even though it flexes. i.e., airplanes,jets,etc. I've snagged downrigger before. just be prepared to loosen drag if this occurs. If you're worried about it, make a small backer plate with some aluminum from home depot and be sure to use quality stainless steel 1/4" neoprene washers on outside(water side) available from duraboat or west marine.