Dear Mr.rovern,

I think, your load combination may have some mistakes. CAESAR II recommend the load and stress combinations for nonlinear case as below;

For non linear case with two vector(X,Z uniform loads are applied simultaneously);

CASE 1 (OPE) W+T1+P1
CASE 2 (SUS) W+P1
CASE 3 (OPE) W+T1+P1+U1 ----total load
CASE 4 (OCC) DS3-DS1
CASE 5 (EXP) DS1-DS2
CASE 6 (OCC) ST2+ST4 ------code stress

For non linear case with each vectors(X-vector 1,Z-vector 2 uniform loads are applied separately);

CASE 1 (OPE) W+T1+P1
CASE 2 (SUS) W+P1
CASE 3 (OPE) W+T1+P1+U1 ----total load
CASE 4 (OPE) W+T1+P1+U2 ----total load
CASE 5 (OCC) DS3-DS1
CASE 6 (OCC) DS4-DS1
CASE 7 (EXP) DS1-DS2
CASE 8 (OCC) ST2+ST5 ------code stress
CASE 9 (OCC) ST2+ST6 ------code stress

I think the sign of dynamic load is not important since it is OK if we just consider the maximum absolute load for dynamic load.
If you want to separate the seismic load only to inform that to civil group, you can add additional load combination, for example (OCC) U1.