I can access the fuel caps from the side of the truck with no issue. That was a priority before I started the build. The top triangle gaps are for access to the fuel return /breather lines that go into the fuel tanks as well as the APU fuel line to the right fuel tank.
When I put the drom box on I used a 3/16 cut out that cover up the access points. The welder, plasma and tool chest is on the right side of the drom while the consumable/ durable storage products are on held on a shelving unit to the left side of the drom box.