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Are you looking for a shop to perform the work? In general, avionics shops will provide the metal panel alterations as part of the installation to include any approvals. But in most cases the panel work is considered a separate task from the avionics install and requires its own approvals if necessary. So in reference to your STC inquiry, are you looking to perform the Dynon install yourself?
I am working with an installer and was advised that the fabrication and approvals (not necessarily in that order) for the panel would be somewhat time consuming. So I wanted to confirm that there is not a pre-blessed panel solution that was overlooked. Thanks.
Which is why you should get 2 or 3 bids to do the work. My gut tells me you can find another installer that won't have a time consuming issue with what you want to do. Just my guess.
By "installer" is this an established shop or an individual person? For context, even as an independent A&P it wasn't difficult for me to find someone develop a CAD file for a new panel and have a machine shop cut it out. Perhaps this level of work is outside the normal work scope of this installer? You could call some larger avionics shops like Sarasota, etc to get a baseline on custom panels, then have a discussion with your installer on why he considers it time consuming unless he still hand-fabricates the panels? Since CNC has gone mainstream, field-level, computer designed/cut panel mods, etc. have become pretty much common place and at reasonable costs.