What you want to do is to turn off the park water, drain all of the water out of the water lines using the low point drains, and drain the fresh water tank.
By pass the water heater, then fill the fresh water tank about 1/3, then pour 3/4 cup of bleach in the fresh water tank, then continue filling with water until it is between 1/2 and 2/3 full, pour another 3/4 cup of bleach in the fresh tank, then fill until you get some coming out of the over flow vents.
This will mix the bleach in the water pretty good.
Now, using the water pump (and the water heater bypassed), open one faucet and run water until you have it coming out of both hot and cold (you should smell the bleach), then do the rest of the faucets one at a time, including the inside and outside showers, plus the toilet.
Now . . . best to leave it sit over night if possible (but no less than four hours).
Then drain the fresh water tank and fill and dump twice, then put however much water you like to keep in there, allowing enough to run out to each faucet using the water pump to clear the bleach water out of the water lines.
Now you can turn the park water back on, but don't forget to turn the water heater bypass off.
If this doesn't work, maybe the smell is coming from the gray tank.
Let us know!
Low point drains:
Hot water heater bypass
(note the red & blue pipe with the valve in the middle):