Yup you can create it in the same level as the struts.xml
here is what my struts.properties looks like
struts.objectFactory = spring
struts.devMode = true
struts.enable.DynamicMethodInvocation = false
struts.custom.i18n.resources=messages
struts.mapper.class=com.springstruts2.web.struts.action.Mapper
struts.multipart.parser=org.apache.struts2.dispatcher.multipart.JakartaMultiPartRequest
struts.multipart.maxSize=102400000
struts.multipart.saveDir=c:/export