Installing New Shower Including Rough In For Control Valve

I am planning on installing a new shower in our cabin bathroom. It is a very cheap kind of shower, but it will do for a cabin. It is a Durastall Model 68 shower and looks like it is a Phoenix Faucets control valve. I have listed the links below. The installation video for installing the shower just says "install shower control valve and shower head" and does not elaborate.

Even if I do my 4" center rough in copper lines inside the wall and drill my holes for the shower control valve shown in the 3rd link below, how do I connect the threaded fittings on the back of the control valve to the roughed in plumbing inside the wall? Without an access panel on the inside of the shower or on the outside of the bathroom wall, I just for the life of me cannot visualize how to connect the control valve to the roughed in plumbing. Any help would be appreciated. Thanks.

https://www.mustee.com/product-lines/shower-stalls/68.html

http://phoenixfaucets.com/store/product/0p1437s

http://phoenixfaucets.com/resources/pdfs/SI-96PX%20mustee%2068.600.pdf

you need 2

brass threaded washers, 1/2'' 14 npsf thread

drill your holes and install the faucet as you install the panel.

then after you are done, sheet rock the wall behind the faucet or install an access panel/ door

Okay, thanks. That makes sense.