rust proofing/undersealing

 Do you think it’s a good/acceptable idea to drill a hole to gain access to the rear sill area with the aim of squirting some rust treatment/underseal in there.What about the area inside the wheel space where the wheel arch meets the bottom of the sill and then sealing it with a grommet?

 If you take the forward section of the rear wheel arch liner out (it’s only a few screws) there is a grommet underneath it (you can see the impression shape in the liner. Take the gommet out and it gives access to that area and you can squirt something in. I even managed to get a small flexible LED reading light in there to take a look. I also take out screws in the door striker plates, the courtesy light switch, sill kick plate cover screws etc and squirt in these to get something in anywhere you can. I would do this before drilling any more holes.

 ok ,thanks for the reply.Good idea .i will try this method first