How do I remove horizontal hull seam?

[Magnus]

I am new to ship modelling. Last week I picked up the Trumpeter Udaloy destroyer "Admiral Panteleyev".

Now I want to build the kit in the full hull configuration, but the hull comes in two pieces (duh!).

What is the best way to remove the seams? Appartently the grey and the red plastic have different charactesristics and when I sand the puttied seam, the sanding paper eats away the red lower hull, but leaves the grey upper hull intact (almost). So I just have to start all over again...

Any hints or tips on how to treat this seam?

TIA

/Magnus