TM    9-2330-238-14 2-21.    OPERATION IN  EXTREME HEAT   (Con’t). CAUTION DO   NOT    use   gasoline or   dry   cleaning    solvent    to   remove oil   or   grease spots    from tarpaulin. Use   only   water    and   a  scrubbing brush.    Failure   to   follow    this   caution    will damage    the  tarpaulin. c. Cover inactive semitrailers with   tarpaulins if   no   other    shelter is   available. Tarpaulins are   subject to deterioration from   mildew    and   attacks    by   insects   or  animals.    Shake   out  and   air  tarpaulins weekly    for   several   hours. Clean   mildewed tarpaulins    with   a  dry  scrubbing brush,   DO  NOT  clean   with  water   until  mildew    is  removed.    If mildew    is found,    examine    tarpaulin to   determine if  it  is  rotted   or  weakened. Replace    tarpaulin if  damaged. If tarpaulin is  not damaged, treat   as  outlined in  FM  10-16. d. Semitrailers, inactive    for   long   periods in  hot,   humid   weather,   are  subject    to  rusting   and   accumulation of fungi   growth.    Frequently inspect, clean,   and   lubricate    to  prevent   deterioration. 2-22.    OPERATION IN  SANDY   OR  DUSTY   AREAS. a. Clean,    inspect, and   lubricate semitrailers more   often   in  sandy   or  dusty   areas   (Chapter    3,  Section    I). b. Maintain    proper    tire  pressure: (1) Reduce   tire   pressure    to  32  psi   (220  kPa)  for  operation in  soft   sand. (2) Reduce   tire  pressure   to  40  psi  (276  kPa)  for  operation    on  cross-country terrain.   Tire  pressure   must  be returned   to  48  psi   (331  kPa)  when   operation resumes    on  hard-surface roads   if  tactical situation permits. c. When   uncoupling semitrailer in  sandy   areas,   use  ground   boards   to  prevent   landing    gear   from   sinking    in. 2-23.   OPERATION IN  MUD   AND   SNOW. a. Reduce    tire   pressure    to  32  psi   (220  kPa)  for  operation in  mud   and   snow. b. Immediately after   operation in  mud,   thoroughly clean,    inspect, and   lubricate if  tactical situation permits (Chapter   3,  Section    l). c. Pack   wheel    bearings as  required    (Chapter   3,  Section    l). d. Refer  to   FM  21-305   for   special instructions on  driving   hazards    in  snow. e. After  each   operation, remove   ice  and  snow  from  underneath    semitrailer and  from   hoses,   lines,   tubes,   and electrical connections, 2-24.    OPERATION UNDER   RAINY   OR  HUMID   CONDITIONS. a. Dampness increases chances of  corrosion. Inspect   all  surfaces and   electrical connections for   signs   of corrosion. Remove   all  signs   of  corrosion. Apply   corrosion preventive    compound (Item   5,  Appendix E) to  all  electrical connections. b. Protect    semitrailer from   direct   rainfall   whenever possible. During   dry   periods, open    semitrailer to   air  to facilitate drying    process. c. Keep  moisture   from  entering   the  fuel  supply.   Clean  fuel  filter  before   each  operation    to  remove   accumulated moisture. 2-25.    OPERATION IN  SALTWATER   AREAS. Clean, inspect, and    lubricate the    semitrailer more    often    when operating in   saltwater areas (Chapter 3, Section    I). 2-33