Slide outs are wired directly to battery ---shortest wiring route/less resistance
30A fuse for slide out blowing due to high amp draw which probably means the two times it blew the battery voltage was low.
How many batteries ---1 or 2?
Water levels ...... voltage reading"
Had you been placing high demand on battery prior to slide out fuse blowing?
How good are battery cable connections....clean tight on positive AND GROUND?
Is slide out wiring connection tight at battery?
A properly charged battery should be able to operate slide out w/o being connected to shore power.