I don't think you're going to find one for the "house", but you should be able to find a service manual for your chassis from its manufacturer. IRV2.com has a variety of chassis forums that may be of help in this regard.
The manufacturers of the various components, heaters, air conditioners, slides, etc. should be able to provide service manuals (or maintain online versions). Other than that, looking for a service manual for the "house" portion of your RV is kind of like looking for one for your house.
The closest you're likely to get from Winnebago will be the electrical and plumbing diagrams, etc., which can be found here:
My advice is to download the items listed in the above link now since you never know when Winnebago may discontinue listing them on line.