Posting XML files and validating response

Hi I am fairly new to the loadrunner scripting and would like some help.

I need to POST some xml files which I am attempting as follow:

lr_start_transaction("BDD_trajectories");


 web_custom_request("BDD_cruise",
   "URL=http://{URL_Param}",
   "Method=POST",
   "TargetFrame=",
   "Resource=0",
   "Referer=",
   "Mode=HTTP",
   //"Body=lr_eval_string(lr_eval_string({xmlFiles}))",
   "Body=lr_eval_string({xmlFiles})",
    LAST); 


 lr_end_transaction("BDD_trajectories", LR_AUTO);
 

the {xmlFiles} is path to the xml files and the {URL_Param} is the server that takes a set of trajectory values from these xml file and sends it to another server (external to our ogranisation) which in turn returns as set of CSV values for the requested parameters, here some smaple input and expected output.

INPUT:

 <wps:Data>
                <wps:ComplexData mimeType="text/csv">lat,lon,height,time
48.7537222222,2.10236111111,500,2015-08-11T06:00:49Z
            </wps:ComplexData>

OUTPUT:

Relative humidity (N_PERC),Temperature (T_KELV),Wind - u component (S_MPS),Wind - v component (S_MPS)
82.92,290.98,-1.54,-2.51

I would like to be able to log/validate the CSV values any help would be appreciated. I have enabled the "Data returned by server" option in the Runtime settings>Log section but can not see in the ouput the CSV values!

thanks