I like 120s and 160's for fisher.120's for marten and hate 160's for marten.

So my best bet would be to make boxes for belisle 120s and 160s, I got some work to do, if you're doing 16 inches deep for a marten box, is that deep enough for a box for fisher or should those be a little deeper?

16 depth should do for fisher also,it will be a bit bigger for a 160 so should be able to pack a good bunch of fist sized beaver chunks in there.

Do you get beaver the year before and save it or do you get it the year of? I don't really have any property that has beaver on it currently. I did see that minnesota trapline has a bucket of beaver meat for sale I'm not sure if that would work okay or not

Find some beaver to trap.
I trap about 30 -40 beaver in the fall season starting mid October.for fur and for bait.I gut them and pile them up in a bait shed/wood shed for use later.Some will taint nicely and some will be fresh.There is use for both.
I imagine deer scraps would work for bait for marten and fisher,should be lots of that available in early trapping season.
I use moose scraps for wolf bait and lots of fur animals are attracted to it.
beaver is preferred because it remains attractive when it gets real cold and its fatty so it doesnt dry out as fast as lean meat.
There are some good marten trappers I know that use butcher scraps for bait.Beef scraps is much better than pork.

I've looked around for beaver I haven't been able to actually find any, I've had one property a couple years ago that had beaver on it and haven't had anything since. Would muskrat work?

Bait like rabbit,muskrat grouse scraps etc work before you get into the deep freeze..
Muskrat is good bait for muskrats and mink.
Grouse scraps work good for lots of different animals,but has little attraction when it gets real cold.
You need to kill a pile of grouse to have enough of it to last beyond the first couple weeks of trapping season.
If you know some beaver trappers they might give you some carcasses to use for bait.
Lots of beaver trappers get way more than they can use.

Sadly I'm the only one I know that traps, I did it with my dad growing up and now I'm trying to do it with my boys to keep it going

I have some old boxes that are longer and made out of 1" rough cut pine and fir. They work good, but dang are they heavy when they soak up water. The tapered boxes I build are 16" deep (you can get three 16" strips out of a four foot wide piece of plywood, then cut all your sides out of those strips) and mostly made out of either 1/2" or 3/8" plywood (I don't remember which) for weight. Although I have a couple made out of some scrap 3/4" I had. I used a staple gun and some wood glue to securely make boxes out of that thinner plywood. The closed end of mine is plywood rather than the wire some use. I drill a couple holes through that for air flow, then I put a short piece of cable with a loop on it out one of the holes and attach the trap chain to that with a caribener. I don't think I would trust that anchor system on a box wired to a tree rather than screwed.

Beaver is great bait, and tainted works as good or better than fresh. But muskrat and other meats will work, just put a good sized chunk in. Rather than wire the bait in my vertical boxes I have went to using a square of rabbit wire that is just larger than the box. Shove that in to hold the bait in and the edges of the wire dig into the box, holding the bait securely and helping prevent bait theft from weasels and mice. Some people have good luck with fish also, but I've never tried it. I usually freeze some beaver to use the next year as bait, because up until this year beaver opened the same day as marten, so it wasn't like you could trap some ahead of time for bait.

Thanks for the advice, how far in the box are you placing your traps and how far back are you placing the bait?

I cut spring slots about three inches deep and slide the traps all the way in, with the bait all the way in the back of the box.

Awesome, all this information is what I'm going to keep looking back to, I can't wait to go next wear, we only have a 9 day season for fisher and marten in michigan and I want to make sure I can connect in that time, if there's anything else you could think of that would be helpful let me know, I'm running out of questions but I'm sure I'll be flooded with them when I actually get out there next year

Kurt, I live in Dickenson county, if you let me know when you will be here, I will save a beaver carcass for you or show you a spot or 2 where you can catch your own. I don't do the marten - fisher thing thing as the limit is 1 or 2 with a 10 day season. You might do well to get ahold of the bear guides in the area and see if the will show you the locations of there baits. Deer meat and muskrat work well also.
Good luck

That would be great, I'll definitely be looking you up, I plan on coming up the day before the season starts and leaving on the last day of the season, I'm not familiar with the upper peninsula at all, I went there on a 4th grade field trip 20 years ago and I was there about three years ago on the east side for a one day metal roofing job and that's been it. I will look into talking to the bear guides also

I went up to the UP of Michigan on a deer hunting trip a few years back.Excellent country up there.Alot like Maine but UP of Michigan still has their cedar deer yards.Here in Maine they have cut 98 percent of them.

I make my boxes a lot more shallow, and tapered to stack. Any plywood you have laying around will work. I'm sure the deeper box/more bait theory probably holds some truth, but I like being able to carry as many boxes as possible with me so I make mine about 7-9" deep the big end is about a 6.5" opening, small end is about 4.5"

How far off the ground are you placing the ground on the vertical box sets?

Whatever height is convenient for me, usually about chest high. Only real important thing is that I want them high enough the marten hangs free without touching the ground, after that it is just a convenient working height.

Okay I didn't know if the height would actually effect if they would come into the box or not

Height of box depends on snow depth.
You want the trapped animal to be high enough from the snow so animals like fox cant chew on them