Chub,I make my floats about 2 feet long.I like to use something thicker than a 2 by 4,4 x4 is better.
I take a board and nail it across the 2 side boards--right across the middle.I then nail lathe across the ends on the bottom.I then take and staple screen to the bottom.
The cross board on the top ,not only makes it stronger,but allows me to place a mound of vegetation on top of it.Along with some lure.
The lathe on the bottom,keeps a trap in place on each end.I mount a cable loop on each side of the float.On the ends of my traps,I have a snap clasp---like on a dogs leash .This allows me to quickly and easily attach my traps to the float.
I attach cable to the center of the float ,and place a weight on the end of it.make sure you leave some slack in the cable,that way the float has room to go up ,if the water rises.
I use floats on bog lakes and ditches,but rivers and creeks would work too.
If you can ,place the floats out before the season,this gives the rats a chance to start using them, and become accustomed to them.
One of the keys with float sets--don't try to compete with natural resting places.
I have had very good results with floats in certin areas,I have also caught several beaver on these floats.They can be a very useful tool ,in the right area.
Tom