Consider using a lot of clamps, or their equivalent.

You have a few options: Nail or screw a block of scrap wood to your forms, directly under where the keel strip goes, and you can use a plain C clamp to hold the strip to this block.

Drill a 1 inch diameter hole in the form,near the edge, but leaving at least 1/2 inch of wood, and you can hook the end of a C clamp into that hole.

If you do not have enough C clamps, use a sabre saw or band saw to cut several "C" shaped pieces from scrap wood. the exact size isn't important, but try to keep the opening in this "C" at about 1 1/8 inches. If your scrap block under the strip is 3/4 inch thick (made from a nominal 1 x board) and the strip itself is 1/4 inch, then you'll have 1/8th inch of extra space to play with. It takes just a few seconds to whittle a wedge from a scrap of soft 1/4 inch thick cedar strip. Poke that in until the "clamp" holds the strip securely. The soft wood wedge should not mark the strip.

Small scraps of 1/4 inch thick strips can be positioned to one side of the keel strip on each form, then another scrap of wood can "bridge" the two pieces (scrap and keel strip). Drive a screw through the two stacked pieces of scrap wood and into the edge of the form. Drywall screws are nice for this as you don't need to predrill a hole for them. Keep the strip screwed down in this fashion until it is securely glued to the adjoining strip. If you are workng away from a previously stripped area, put glue on the edge of the keel strip, slide it into place, and clamp it down (or screw it down).

You may need to clamp down several strips on each side of the recalcitrant keel strip until things lay flat on their own, or with the aid of minor amounts of hot melt glue.

Best of luck.

Paul G. Jacobson