I guess I suggested toggle bolts because they would allow inverter mounting without needing access to the top side of the bin, like a bolt and nut/washer solution would require. I was also concerned (after thinking about it) that with toggle bolts, you have to enlarge the bin holes to get the spring loaded toggles through (then they pop open on the top side)......but, if the space on the top side of the bin is subject to road debris and water intrusion you might also need to add a large rubberized metal flat washer (or separate metal washer and rubber washer facing the up side) on the “inner” top side of the bin.......to act as a seal at the mounting hole openings. If you are concerned about toggles cutting through the bin top, perhaps taping the toggle arms a little prior to installation would help prevent any toggle metal edges from cutting back through the bin top.....although I would think once snugged up, the inverter would not move very much. You could also file any sharp edges on the toggles prior to install.
Probably a suitably thick piece of pressure treated plywood on the top side of the bin, that would accept inverter mounting screws (suitable for use into treated wood) would be a solution too, but I "assumed" that you don’t have easy access to the top of the bin from underneath the coach; and that you also can’t slide a piece of treated plywood into that space either.
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