Just about any trap made can be used to get muskrats. Many are much more effective than others. The 110 conibear, #1 stoploss, and the 1.5 coil are in my opinion, the best for rats. Where legal colony traps can be a real bonus for the trapper.
The 110 can be used to cover the entrances to the underwater huts or burrows that they use. They can also be placed in rat runs with good results. As you are walking down the creek, those underwater holes that you may sometimes see are probably rat den entrances. As far as the above water huts, They are not real common in most of my areas because they can use the banks to den in and it is believed that the bank dens are more secure for the rats. The lodges are usually found where the banks are relitively low or of a type that is not real great for digging. They are made out of whatever the rat can get it's grubby little paws on, it could be cattails, rushes, corn stalks, trash, and just about anything you can imagine.
The rat is a small rodent which is (on my line) about 3-5 lbs and about a foot long with a long vertically flat scally tail of slightly less in length. I have some big rats on my line for some reason.
Many of the rats that I get are caught as incidentals in coon sets. They will eat the same things that a coon will. They have been seenpiling clam shells on sandbars that they have eaten. One of the baits that has worked well for me on them is believe it or not, muskrat chunks.
As far as where they come out of the water, If there is a above water hut, there should be a trail coming out of the water onto the top. On the stream bank they will make little dugouts under overhanging brush and grass. These are what are known as feedbeds. If you set a trap on the approach(s) to these you should get them.
One thing that is very inportant to remember: in the rat marshes, just because you see the bottom 2 feet down DOES NOT mean that there is not 6 feet of loon crap.
One more thing, ALWAYS try to drown all rats you catch.
I am getting tired of typing, so someone else can take over from here and agree or disagree with me.