My house is a 1960 Cape Cod, with hollow dutch lap vinyl siding over the original wood siding. I wanted to mount a 45-degree flagpole bracket to the side of the house to hold a 2.5x4 foot flag. To support this, I purchased a mounting block (specifically Builders Edge 130110008123 Surface Block) which conforms to the profile of the siding. I mounted the flagpole bracket against this block using 4 2.5" wood screws which penetrate the bracket, the block, the vinyl siding, the original wood siding, and I assume the plywood behind.
This works relatively well, however the screws loosen and work out over time. I have a few times over the past couple years needed to remove it, fill the screw holes with toothpicks+glue, and redrill. I think the problem is that I can't tighten the bracket completely, as is begins to crush the hollow vinyl siding (the profile of the mounting block helps this a bit but not completely.) This means there is some movement in the breeze (I try to take the flag down in heavy wind, but I'm not always home for it and moderate wind still moves it quite a bit.) One thing I tried was spraying some expanding foam behind the siding to add some support, but that didn't actually help much.
Has anyone had/solved this problem? One idea I had was opening the affected siding panel and putting some pieces of wood (furring strips?) inside the problematic bays. In my mind this would let me tighten the screws much better, as there would really be something to tighten against. It would also give the threads some more wood to hold onto, whereas before the threads in the void under the siding weren't doing anything. Is there a problem with this solution?