As you may know, when a wooden ship is planked with the first course of planks, there is a need to sand and fill up all the holes and imperfections due to the inability of the wood to properly bend in the desire orientation.
So, what I have been using as putty to cover those areas is a wood putty that comes in powder form, which is good because you mix the amount you need with water and it become a paste that is fairly easy to put on, you just have to work fast because this stuff drys very quickly.
It is a wood putty, so it is comparable with my wood models, as you may know, when you buy already mixed wood putty, the unused putty left in the can dry up within 20 days so you are always trowing money away, with the powered putty , you only use what you need and as long you close the can, the left over never drys out on you.
Following is a photo of the can. You can buy this stuff in Home Depot or Ace. Lowes most likely also have them. It is cheap, between 8 to 20 bucks, depending on the size
Hope this helps.
Joe