Loosing all the coolant

[turbo4vL]

I am having a problem with our 07 6.0 with 42000 miles and cant tell what the problem is, either HG or EGR cooler. It keeps loosing all the coolant from the resivor when you drive it. Like a 80 mile round trip will use a gallon of coolant. There is no coolant in the oil, temp stays good, and it runs normal. It started when we were pulling our travel trailer back home and under a load (like going up hill) the cab would smell like antifreeze bad. any insite on where to start looking for problems. Also under the hood, right above the resivor tank cap, it is all whit, like it has been sprayed with antifreeze. Possible that the cap is just bad. Me and the truck are stuck at a trailer park 3 hours away from a mechanic, so Im kust trying small fixes my self before it is towed home

thanks