Finally, the first bottom panel is dry-fit.

In the end, I wound up not removing the panel to trim it after all. Instead, I trimmed and fitted it in-place. This method is a tedious and painstaking process, but I found that it worked quite well. The key, as with so many aspects of building a boat, is to take your time.

A “multi-tool” oscillating saw is really an indispensable tool in this process.

First, I had to tackle the transition joint. This really wasn’t too difficult. I had already determined where to place the transition joint, and had sanded & filed its portion on the side planking. Using the crayon-marked line on the inner surface of the bottom planking as a guide, I marked and cut a perpendicular line near it’s aft end. By sheer accident, I got very lucky, and this perpendicular cut wound up being dead-on for the transition joint. 

The crayon-marked line on the inner surface of the panel shows the position of the side planking.

The next part of fitting the transition joint was to cut away enough of the horizontal line to begin fitting the butt-joint between the bottom planking and side planking. I did not have enough working room to cut from the inner surface outward. So, somehow, I had to transfer that crayon-marked line to the outer surface of the plywood. To do this, I simply used my handy spring clip. I clipped it onto the edge of the plywood, then visually aligned the clip’s edge with the crayon line, then marked the plywood along the clip’s outer edge with a pencil. I used the multi-tool to cut along this line, and to remove the excess bits of plywood. I continued this process, about 1-1/4 inches at a time, until I had enough cut away to fit the plywood to the chine and screw it into place, forward of the transition joint. I used the multi-tool saw to bevel the plywood edge as needed for fitting.
 
Next thing you know, the transition joint was done.

Fitted transition joint.

From there, I used the same “mark, cut, fit” procedure, inch-by-inch, all the way to the stem. I continued to place screws with plywood washers every 6 inches along the chine, stem and keel. It took a while, but in the end I was pleased with the fitting.

The panel's fitting along the underside of Frame #2. So far, so good...

Making inch-by-inch progress forward of the transition joint.

Almost ready to fasten to the stem.

Finally fastened to the stem.

Overall, I was pleased with the fitting along the chine.

I was also pleased with the fitting along the faired surface of the stem.