incubator from wine fridge

I need some imput on this it is a 50 bottle unit maybe 7 cuft. I gutted it and moved a wall so to speek in back this back area is like a false wall where i can put the tape and there is a fan already mounted on wall. So what way should i direct flow of air. Have it pulling air from cold bottom moving it over the heat tape then out the top. Or have the warm air from top of fridge pulled over tape and pushed out the cool bottom. To me the first method makes more sense. Also how many watts per cu ft do u recommend for heat tape. I was gonna do 11 inch but if i do 3 inch i get more watts and less space is used. total system would be 140 watts . If i ran 11 inch the whole back wall and floor would have to be covered and then some with 3 inch obvious more connections but all tape would b hidden behind wall. What do think this is the first one i built so any imput would help alot