You can view the M file that is used to create the rtwtypes.h file by executing the following command
>> edit([matlabroot '/toolbox/rtw/rtw/genRTWTYPESDOTH.m'])
You can see what the necessary arguments to the function are by setting a breakpoint in the M file and then generating code.
With this information, you should be able to create inputs to manually call genRTWTYPESDOTH once such that it generates one header file with all of the defined types included for your multiple models.
Alternatively, since the rtwtypes.h file is not too large and should not change, you can combine the multiple rtwtypes.h file once by hand and then always use that custom file in your larger project.
