If your DT is a 75g, I would bet it will drain around 4-5 extra gallons into your fuge in the event of a power outage(5g to be safe). My DT is a 55 gallon and it will drain around 3 extra gallons when I turn the return pump off. So, if you fuge is a 29g, just set up the lowest baffles to be around 24 gallons in the tank. Without seeing your actual 29g, I would assume that is 6 inches below the top of it.
As for your skimmer, is that an insump skimmer, or HOB. If it is in-sump just make sure you make the first chamber large enought so it can fit in the chamber. Then put a 1-1.5 space between the first two baffles. As for the return chamber, just make sure you have enough room to fit your return pump, if you are using a submersible pump. You can get the baffles cut to size from HD, and then just silicone them in.