Before extending the sides I drilled the hole for the starter pull string. It took a little effort to get the angle correct so the rope does not chafe on the wood.
To extend the sides of the fuselage I stapled a straight piece of plywood along the slanted fuselage side.
After carefully adjusting the depth on the router I used it to remove the plywood from the underlying RS-10
Now the plywood extensions can be glued onto the ledge created by the router.
To support the extensions two diagonal braces were added.
Because there was little glue area I added a gusset block.
Lastly some plywood was added on the inside so there are no ledges for debris to collect.
Now I can start fitting the fiberglass parts.
All that remains is to fit the fiberglass parts and fasten then in place.