Skip the RV dealers and find a good, local truck shop experienced in your brand of chassis. You'll be far better off with them than a dealer.
Assuming that it's been well cared for, hopefully it's mechanical condition is good. With my 2002 w/55k mi, I didn't have any major mechanical issues:
1. Two broken spark plugs - replaced all of them.
2. One bad spark plug wire - replaced all of them.
3. Oil change and lube
4. Replaced shock absorbers
The biggest problems I had were:
1. Leaky skylight which I replaced and had to repair ceiling damage in the bathroom.
2. Leaking hydraulic hoses on front HWH slide. This is a known problem. If one hose is leaking, replace all of them, it's much more efficient labor-wise and will save you money and headaches in the long run. HWH had a problem with their swaged-on hose fittings in the early 2000s. I don't know if the '04s were affected or not. Replacements are available from HWH and there is a code number on a white label on each hose. The lengths and specs are critical so best to just order from HWH.
Also, check for windshield leaks, which is a common problem with Winnebagos of this vintage. There are a lot of postings on Winnieowners.com regarding this. In many cases, a strip of Eternabond tape over the top edge and a few inches down the sides (the top tape should go over the side tape, like shingles) of the rubber moulding around the windshield will fix this. Therefore, if you see water dripping down the inside of your windshield try this first. You can try a temporary fix with Gorilla tape before going the Eternabond route. If you have this problem and let it go, you're in for expensive issues. This is also a good preventative measure even if you don't currently have such a leak. The nice thing about this fix is that it's not going to mask another problem. My advice is to not seal the bottom edge of the moulding, you need to provide an exit path for any water that does get in.
You'll also want to consider upgrading your converter/charger to a one with a multi-stage charging function. You will extend your battery life by doing so. Just be careful about the wiring color codes. Here's a link to some issues I had when doing this: