I removed both panels and cut sections out. Then I framed the openings and installed plywood panels. At first, I had wood tabs to secure the panels, but later changed them to barrel latches. These allow me to completely remove the panel without having to empty the basement. The one with the vent (vent was OEM) has the converter and suppressor behind it, so I can easily access both. The other allows access to the water heater and back of the UDC. It also makes it easy to inspect the majority of the plumbing for leaks, especially when using the tank flusher.
Before cutting the panels, I first decided how big I wanted the access openings and scored the fabric cover with an X. I folded the fabric back behind the panels and used spray adhesive and staples to hold it, so the edges of the chip board are covered. The framing was cut to give a lip to place the removable panel against.