I know guys that use heaters in pop-ups....they say its fine....just be sure to get the right one.....no flames or red hot radiant type heaters......Cabelas and T.S.C.,...have one called....MR. HEATER....its has low oxgen cut off switches and other safety stuff....its listed as safe in blinds...I'm gonna use one to take my 9 yr. old out in brickhouse house blind to video some......it just gets too cold here in Ohio too quick.......heck I can't draw a bow with 50 lbs. of clothes on much less hit anything if I could....I don't hunt here much after NOV.,...its too windy and cold......forget treestands you'll freeze solid to a tree....I only bow hunt so I need to be able to draw a bow back.........just be careful which heater you are looking at......p.s. my kid doesn't sit still while freezen his butt off doing nothing......it has to be comfortable and fun......heck I don't care if we shoot any....its about just being there and if we see anything thats icing on the cake......I smoke too and have stomped cigs out just in time to shoot a buck......really funny when that happens.......last time I panic drop the cig off my treestand......deer stoped and looked from 15 yds.,.....drew my bow and nailed him......too funny, I've done it form the ground too.