Does it really matter if a few pounds of excess weight creep into your build?
Rowed Trip, Colin and Julie Angus's account of their voyage from Scotland to Syria in his-and-her Expedition rowboats, sometimes towed by the mountain bikes they were able to pack aboard, made me a weight-loss fanatic.
Then I discovered you can't chop weight until you know the limits.
I built my Expedition and rowing unit from kits during the pandemic lockdown. I used carbon fibre wherever I thought I could cut weight, but it was a hassle to find components that didn't come with the kit. I ended up repurposing discarded curling brooms for the carbon tubes I used as crosspieces in the cockpit box. The sides were 4" meranti ply with single laminations of unidirectional carbon inside and out.
After two seasons of regular use, the aluminum seat rails were showing uneven wear; I discovered the box was flexing in heavy conditions. My second attempt uses Alaskan yellow cedar for the 1" square tops and bottoms. I used eighth-inch oak ply for the sides with a single layer of unidirectional on the insides, fibreglass on the outsides.
Box #1 weighs just over seven pounds — 13 pounds with the seat, rails and stretcher. Box#2 came in at eight pounds, 14 with seat, rails and stretcher.
I'm curious as whether others think 
weight is a concern and how they address it.
