You are probably familiar with the idea of bowed cauls. They allow you to place even pressure across a carcass surface where you would not ordinarily be able to get a clamp for glue ups. I made a couple 24" ones awhile back and find them useful for many things including the most touted benefit; reducing the number of clamps required to do a job.
All that aside, I needed a couple more with a little more oomph so I thought I would share the process. I use some scrap material about as long as the caul will be. Make a mark to use as a reference for the midpoint of the caul's length. I use a shop made fairing stick to select my curve, draw a line from the mid point of the desired caul length to where the stop block will be. Sand to the line to create a template that is slightly more than half of your caul's length.
I attach a support block for the rear edge and a stop block to register one end. The rear support is set back from the edge of the template the distance that will translate into your caul's height at the midpoint.
The curve runs from what will be the midpoint of your caul length to the stop block position and beyond to allow a smooth transition of the pattern bit. Rough cut the caul blank to width but cut it precisely to length.
Run the template from a little more than the halfway mark through one end of the caul to cut half the curve. Flip the blank and repeat for the other end.
On these two I wanted about 1/8" of rise at each end over 24". The clamp is just snug enough to hold the caul still for the photo.
Sorry for my photographic skillset (or lack thereof), you can sort of see the gaps at each end in the pic on the left and then I give each clamp a couple turns in the pic on the right. Surprisingly little clamping effort is required to bring it down tight and it really spreads the pressure out nicely.