I don't know if this will help but I found it on www.forestriverforums.com
. You might check it out as it's specifically for owners of Forest River products.
"We have 2011 350 and our water pump is hidden behind a black plastic panel located in one of the back (3rd from the back I think) compartments on the passenger side of the motorhome. The panel has two of the 5" diameter removable covers installed into it. I removed this panel and leave it at home as I can't for life of me think what purpose it serves other than to possibly insulated the area during the cooler months. I use the compartment now to store all my hoses and some cleaning supplies."