Both the electric and propane are separate systems, and both will heat your water sufficiently. But, to heat your water faster (like back to back showers), you can definitely use both sytems at the same time.
If you are at a campground that provides electricity for free, use their power and save your gas.
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Chap , DW Joy, and Fur Baby Sango
2017 F350 Lariat CCSB, SRW, 4x4, 6.7 PS
2017 Grand Design Reflection 337RLS