I have a 2011 Sundance RLS310 and have the same problem. Got frozen in the big storm in Texas last month.
I guess the best plan that I can think of is to cut out around the current valve then make a new piece to cover the hole with the valve attached.
I got this from one of the posts with the picture of the shower valve with a panel like this idea.
My access would be through the wall in the living area behind a cabinet where the TV is mounted. I removed all the screws but it is still attached on the right side somehow so I think the panel is a much better option. What do you guys think?