I have the same camper in an '88 and I am in the process of summerizing using Hutch's process. I ran into a few issues with my system as I went through his process. I found the valve on the back of the toilet was leaking, then once I fixed that, the hot water heater leaked. I just finshed the HWH replacement tonight and everything works great now.
My advice to you is to keep a close eye on all the water lines, faucets, toilet, (basically the whole water system) as you begin to fill and pressurize the system.
You might also consider installing a hot water heater bypass if you don't have one. This will make winterizing much easier. I added this as part of the HWH replacement and I am very glad I did. They can be had at any local dealer or online. You could also by the parts and build your own.
A link to the bypass:
Here is a post related to that topic:
I hope you have better luck than me. Have fun!