If you are talking about the velcro bags that attempt to seal up the openings under the slide, they are to allow the slide box floor to move around the plumbing going into the grey and / or black tanks. The plumbing is fixed into the tank so the slide has to have an opening to move around it when extending and retracting.
I measured the openings in our SV34 and had my wife make a couple fabric panels. I had her sew Velcro around the edges and then I stick them up on the underside of the slide when we setup to cover the openings better than the bags. Then I remove them before retracting the slide.
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