If you wanted to use two tanks, the easiest way to do it is to drill both tanks and put a bulkhead in, then install a pipe joining the two tanks together.
I've also seen it done where people just hang a U-tube over the edge of both tanks, and the siphon keeps the water levels even... but if the water level ever should drop to where the siphon breaks, you'll flood.
A 29 split in half will give you two 15g sections, which will make for a decent fuge and you'll be right at 10%.
Here is another thing you could do...
Put a 29 on one side, as your fuge, then put a 20L on the other as your skimmer/return. Then take advantage of the 29G's extra height to simply drain over the top into the 20L return section by just intsalling a bulkhead and elbow.
This will allow you to divide the drain from the tank into a skimmer and fuge section, allowing you to control the flow through the fuge, and having a separate skimmer section allows you to keep the skimmer from skimming fuge effluent, something you don't want.
I attached a professional-looking graphic to illustrate.
Though if you aren't in for the effort, a 15g fuge should be sufficient, but this would allow you more flexibility if you want.
