Without seeing the type and size of the crack one can only guess . . . However, as a retired Navy pilot and Aircraft Maintenance Officer the advice given by dscluchfc is sound. Generally a small hole drilled at the very end of the crack will stop the progression of the crack. It's known as stop-drilling and it is a very effective method of halting the crack.
Actual repair of the crack is another question, better dealt with when the type and extent of the crack is better known.
Old trucks and old trailers . . . a comfortable combination!
A-6E All Weather Attack Driver, BUFF
USN Aircraft Maintenance Officer, Ret.
'91 Suburban R-2500 w/BBC
'78 Honda GL-1000
'72 Triumph T-100R Daytona