i would reccomend next time leave the skin on. whitefish are super oily fish which makes them a super smoking fish. one of the best, better than salmon IMHO. them and laketrout have to hold top honors and they are both very oily fish. and they are very good for you as this "fat" is very high in omega 3's and 6's...
i would do a brine and probably do a small batch and start out with say an 8 hour brine time. they are very delicate fish, its not that they are mushy, its the oils in these fishes make up which gives the flesh that appearance and texture. be gentle with them, even hard running water can wash them apart. do not rinse, run the cold water first and then carefully soak and rinse in the water.
you could oil the racks and try it like that but i think if i were doing it, and this is just what i would try, i would cut a piec of foil same size as fillet, using a fork i would make a bunch of holes in the foil. then i would use some evoo on the foil and place the fillet on it and smoke as usual. so basically a replacement skin.....
here is the brine i use and feel it is a very good one and many whitefish have been smoked in this brine. good luck and be sure and do a thread and post pics on this.....
smoked fish brine
2 3/4 cups pickling salt
10 qts cold water-use good water
1 cup brown sugar
2 tbls garlic salt
soak avg sized pieces 24 hrs, soak in fresh water 1 hour
big thick pieces of fish, may require more time and smaller less. once out of brine set on a rack with a fan blowing across fish til outside of fish dry, a coating will form on it called the "pellicle", is now ready for smoker. i also like to rub some brown sugar on the meat