To get the value of the last low of a lower bar (including an outside bar) use the VALUEWHEN() function:
V1 = BARTYPES().Lower or BARTYPES().Outside;
VALUEWHEN(LOW(),V1)
So the stop formula would be when the low value of the lower/outside bar is lower than the previous:
// Identify lower & outside bars;
V1 = BARTYPES().Lower or BARTYPES().Outside;
//Get the low value when V1 is true
V2=VALUEWHEN(LOW(),V1);
//Signal when low is lower
V2 IsDown
The blue line is the low value and the red Show Bars are when they are lower: