Do I need access under the bed in the 178?

The water heater is under there, and you do need access to it twice a year. You can either just remove the whole under mattress panel as needed, or cut that panel so you only have to open the section over the WH..

You have to winterize and summerize your pod water lines.

You need to operate the bypass valves BEHIND the WH, unlees of course you want to use 7 gallons of anti freeze to winterize. By bypassing the WH, your system will not have to fill it with AF before it can fill all the hot water plumbing.

I don't know if you bought your pod winterized or if you paid to have it done, but if done properly, those valves will have to be accessed and turned before your WH will work right.

Once again, it is far easier to blow the lines (and water tank) free of water using a small air compressor and one of the new "blow out hoses" sold to connect the compressor up to the fresh water fill connection.  I have used this method for about 20 years.  The only antifreeze needed are small quantities to fill the sink and shower traps and a little in the upper part of the toilet.  Total antifreeze needed is about 1/2 gallon.  There are several threads telling you how to open the low point water line drains, how to drain the water heater, the fresh water tank, etc.  Equally important is using the right amount of air pressure, but this is also covered in several other threads.

I have no reason to open the sealed areas under my 2014 178.  If a problem should develop, I think I would cut an access to the problem through the rear storage area. 

Bob

mmmmm.... fresh oranges.....