Ray posts a lot on the oldgmctrucks.com page. He is also a member here and has sold lot's of panel patches. Several years ago, I sent him the rear cab corners for patterns and a few other guys have provided him with other patterns.
Here is a post from him regarding patch panels and how they are installed. You may have to join if you are not already a member.
INSTALLING RAY'S SUBURBAN/PANEL REPAIR PATCH PANELS INSTALLING THE REAR STEP SILL REPAIR PANEL Here's his shop that Rob English took pictures of. Rob has done to OLDGMCTRUCKS.COM as John Milliman has done to the STOVEBOLT.COM. They are like brother sites, sometimes brotherly rivalry but brothers still the same. Both excellent sites for us to learn and enjoy!
RAY'S SHOP I will check with Ray to see if he can put together an informational page for stovebolt fans too.