Typically you can adjust seat height or angle by adding some washers on the mounting bolts, between the seat frame and the floor.
Addendum: Now I realize it is not the tilt angle that needs adjusting. Probably not much to be done about the other angle. I suspect the chair is square with respect to the chassis but the dashbaord is angled slightly in front of the driver, perhaps slightly curved, making the seat appear to be off.
The water heater is easily located - simply turn on the LP gas mode of operation and listen. Then go outside and locate the access door that covers it - it pops open easily, usually hinged at the top with a single snap lock at the bottom.