What works for me about the marruage is that it still seems more of a friendship than a marriage, except that they sleep in the same bed more often. Neither character is particularly romantic or given to declarations of passion, and it could easily be read as a marriage between two asexual characters. The relationship remains based on a deep mutual respect and shared inclinations for adventure. The marriage aspect, once established, doesn’t impinge much on the actual events. I’d enjoy the novels a lot less if the relationship were more romantic, I think, but it’s solidly companionate.