[JRTJH]

I do not have that trailer and have not seen one to verify this, but the water heater bypass is at the bottom of the plumbing behind the water heater at the cold water inlet to the water heater. It will look something like these photos and the valve may be inside the PEX pipes or outside the PEX pipes, so you may being it on the outside of the bottom cold water inlet or between the plumbing and the water heater, effectively, so well hidden that almost everyone would miss it at first or second glance.