Changing out direct vent waterheater

I need to know if I can replace a direct vent waterheater in a mobile home with a regular mobile home water heater if I put a vent in the wall to my washroom so it can get air.

I would call a plumber for the replacement of the water heater.
You do like waking up in the morning and having the trailer intact don't you?

This is a gray area as far as what codes may apply. But the important thing would be to provide proper combustion air. If the WH is located in an enclosed space, it needs a vent inlet within 14 inches of the floor AND and inlet within 14 inches of the ceiling. Each of these needs to be about 1 sq. in. per 1000 BTU of the water heater if taking fresh outside air, and about 4 sq. in. per 1000 BTU if taking air from inside the home. Naturally, you need to run a flue pipe straight up through the roof, observing proper clearances to combustibles in all directions.

If you do not already have a carbon monoxide detector in the home , we strongly recommend this for all homes with fuel burning appliances.