In my Navy days, For about the same size mattress the Navy had a sheet or "SACK" (sailors had another name for it) that you inserted the mattress down into with little tye-tyes at the top. It was like a well fitted pillow case. When one side became soiled, you simply flipped it over for another weeks of use before taking it to be laundered.
Also in my last TT/BH, I had two dark green vinyl covers made to keep the bunks clean when not in use.
Sid, Lois & HRH MISSY Terrible 2s SHIH TZU
2011 ROCKWOOD 8285 WS
2014 F-250 KING RANCH PS/SD/6R140/BFT
BOLIY PRO 3600SI GEN
DAYS CAMPED 2016 57 DAYS