Hi ShadyAcres87,
Welcome to the posting side of being a member of the Heartland Owners Forum.
We always keep the slides closed when the rig is in storage. We have slide toppers which would keep stuff from collecting on top of the slide outs, but I don't think I want the Texas sun beating down on the fabric. I'm not certain about the possibility of water intrusion, but I would expect to be more vulnerable with slides open than with them closed.
Less likely, but in the event of a failure of the slide out hydraulics or electric motor(s), if the failure occurs with slides out, you have to get them in before you can tow to a service location.
Others will no doubt have various opinions.