since I have been doing this going on 40+ years i can tell you borax for our feathered friends and salt for mammels and such. borax the bird skins and place between sheets of newspaper, then add a weight on top and let sit for a week or 2. animals take longer to do, make sure you flesh (scrape all fat and meat off) then stretch skins on boards and add a coating of salt. stand on end and place some cardboard under to collect fat, blood and water that runs of. once dryed 2-4 weeks you can store in a dry container. I use moth balls or crystals in my containers to keep any other nasties out. as for the bugs on a carcass once it cools off they will die or leave looking for another host (non-human) so freezing and nuking is not nessasary. if the is a lot of blood and dirt you can wash first in a mild detergent (dawn for dishes is great) then pat dry and continue with the preserving process. for loose feather just place in container and add a little borax or mothcrystals done