I have been using standard portable hot smokers for years and sometimes when I’m smoking the bottom steel holding the sawdust ‘pops’ with the heat and sends sawdust over the fillets on top.
Any remedies or suggestions?

Mine did that too..... a real pissoff . . I just stomped my boot into the bottom thus deforming and slightly creasing it ..... end of problem . I also only use one burner and leave the lid   so there is a 20mm gap at one end . I find the smoker is real easy to overheat , like if your getting black tarry looking stuff dripping off the underside of the lid  ( and onto your fish ) then its getting to hot ..

I am thinking too much heat. Have used that system for decades and not noticed that.