I use Debbie Browns madeira cake often. I use real butter and it is still a little dry. But I use a lot of buttercream on it and that helps. It is just the BEST cake for carving, so I keep using it. I found that it should be wrapped in greaseproof paper or clingwrap as soon as it has cooled down enough and that improves the moisture. For regular round cakes I use box cakes and it has surprised me time and again by how moist it can be.