Built-In Cabinets on a wall with Vent

meeyuu226

I'm to get some good piece of advice on a project I'm thinking about doing.

I have a 12' wall in my dining room with two 27 inch windows. In between the windows is a wall with a cold air return near the floor-- a small one -- my house is old and doesn't have a central cold air return with a big opening, just small ones all around the house. This cold air return has been somewhat blocked off by a cabinet (36") that is used as a stand for a salt water fish tank.

The tank maintenance components (pumps, water filtration systems, sump,etc) has outgrown the cabinet, and now i'm thinking about building an built-in unit that goes all the way across this wall. Below the two windows would be benches with lids, and then a sturdy cabinet where the current cabinet is to hold the tank.

What can I do about this return? Is it possible to extend it into one of the benches? Relocating it completely would be a big project, wouldn't it?