IMO if you want to keep LR and chaeto in your fuge, then don't try to keep a DSB ( or regular ) in there. it makes it almost impossible to properly maintain the sandbed and nasty things will start happening. what is good for the sandbed is bad for the fuge and vice-versa, if possible it's best to keep these two separate.
when i moved my system ( 3 - 4 years ago ), i added a sandbed to my fuge because i only put about 1" of sand in my display. it worked ok because i had easy access to make sure the sand wasn't getting clogged with detritus. about a year ago i moved some LR into the fuge, making it a big pain in the butt to keep clean, or even see what was going on down there.
a while ago i decided to clean out the fuge, here are a few thumbs that show the fuge before, the water after removing all the sand and rinsing the LR and how it looks now. there is a tonne of life crawling all over the LR and living in the chaeto, so i don't think i lost that much life and i have sand in other parts of my system, so those dwellers have a place too.
