I used to spring rat trap on a large marsh by S.E. Nebr standards after ice out in the early 80's. A few have mentioned about the huts collasping in in the spring. I found 110's and colony traps about useless in the spring. The huts are all undercut benethe the water line and runs are all mucked in w/ dead cattails. No well definded hole can be found on these huts after ice out. I made some fast, big rat catches off these huts with legholds. I would just set on sign, their toilets on the side of the hut or little feed piles that the rats made when feeding on side of hut. If none are present, what works equally well if rats are still present, is to just dig a small pocket into the side of the hut about 6-12" deep, bed trap in water at base of pocket. the rats will come and try to plug the pocket and be caught. I saw Don Bolte and a partner catch 2600 rats in 3 weeks doing this out of a boat. The next year I got smart and got a boat an was able to get just under a 1000 doing the same thing. I ve found lure or bait really had hardly any affect on the set. I stopped useing lure altogether on these pocket sets. Seems like you usually get 60-70% the first check, 40-50% the second check and down to about 20-25% the 3rd check. Move after 3 days max. I would get about 10-15 days open water trapping before the damage from fighting would make you quit. I would have 50% heavy damage after that. If ya can get out just before the ice goes out, the south side of the huts will have some open water from the sun. You can get an extra week of trapping if ya can get on the ice at this time. Those rats on a big marsh w/ a high population will ready tear each other up real quick so you got to get after them quickly after ice out. Creeks and rivers dont seem to get as intense of fighting and the rats will last a little longer. I would look for those grassy banks where rats feed and dig a pocket and stuff some green grass in it, lure would help on the river in these sets.Little undercut feed stations, slides and toilets are still the best, but sometimes sign is hard to come by if the water has risen on the river. There usually is a fair amount of rat activity near the grassy banks as this is where they will be feeding. I never had that great of luck w/ floats, they seemed to sink after a few days, and was a lot of work to haul many of them for such a small payback, but I wouldnt doubt there is a way to make them tick, I just never found it.
Rich K