Coating inside keel

Quoting from the designer notes " Internal voids (rudder, skeg, fairing piece) to be filled and drained with bitumastic paint."
I had some of the stuff they used for underground pipelines and brushed it on internal surface of keel plates to roughly the height of the ballast. Now I want to coat the areas above the ballast line up to the access plates. Common sense tell me to use bitumastic again, however, the quality product I used before is not available anymore. I can get a quart of asphalt primer in Home Depot which can be used for underground steel and concrete. There are corners where I can't get to even to power brush it. Or should I buy epoxy paint, whole gallon of it. The asphalt primer covers everything while even the low maintenance epoxy requires a bit better surface to realize the cost/quality advantage.
The keel is going to be closed with bolted access plates so the only moisture possible down there is condensation for which the bitumastic should be good enough. Perhaps I can fill the remaining void with expandable foam after the ballast is in. Now I am thinking, will the foam stick to it?

 

It's important you check for compatibility with the next coating you apply. Bitumastic paint can come in a few different forms. The usual stuff is an asphalt base, but coal tar epoxy, polyurethane and acrylic bases also have worn the "bitumastic paint" label on the can. Find out what it was previously and use a similar or compatible coating as your project continues.

 

Compatibility is the key. We have all made expensive mistakes. The worse thing is to have a sticky mess that is almost impossible to clean.