Treating inaccessible area?

[347sixtyseven]

Hello,

Wondering if you could give any recommendations for treating an area that is inaccessible for wire-brushing and other such prep-work?

There is a small amount of mainly surface rust inside the cowl area of my mustang and i am after a treatment that will buy me some time before having to cut the cowl open.

The following is a picture of an intact cowl

The following pic shows a cowl with the top end section cut away

Mine is probably the same level of rust or a little bit worse than the second pic. There is just enough rust to allow a small amount of water to get through the old sealant between the cowl base and the upright pipe part. So i am basically looking for some way to seal the area. I was considering pouring something in that would dry in a thick layer across the bottom and thereby prevent water seeping through.

You can see on the first pic there is a small amount of access through the drain hole on the bottom right as well as access up through the vent tube as can be seen in the second pic.

Any suggestions would be greatly appreciated.

Gary