My preferrence is for factory manuals. Some of the older ones are out of print and I've had luck on e-bay. Be sure you get the right year manual. The chassis year is not necessarily the motor home year.
Take a look at your VIN number. It will look like 1GBKP37W6E3123456. The numbers in order mean:
"1" for US Built, "G" for General Motors, "B" for Chevrolet incomplete (they just made the chassis, not the Motorhome), "K" for 14,001 to 16,000 GVWR with hydraulic brakes (an "H" in this position means 9,001 to 10,000 GVWR and an "J" means 10,001 to 14,000 GVWR). The "P" means Forward Control (Steering wheel and other controls are in front of the engine), "3" for one-ton rating, "7" means motor home chassis, "W" means 454 CID, the next number (6 in this example) is a check digit.
The next position gives the model year - in this example "E" means 1984. an "F" is 1985, a "G" is 1986 etc. The following number ("3" in this case means it was made in Detroit). The next numbers are the serial numbers.
So is yours an "F" or an "E" in the model year position?
If it is an "F", you are looking for a 1983 factory manual for the 10-30 series ( there a 1983 manual on ebay at http://cgi.ebay.com/ebaymotors/ws/eB...category=34216
). If it is an "E" you are looking for a 1983 manual (see ebay: http://cgi.ebay.com/ebaymotors/ws/eB...K%3AMEBWA%3AIT
You might also check helm.com for new, factory service manuals (although some older ones are out-of-print).
Another source is one of several bookstores selling old manuals. Take a look in a Hemmings magazine -- there are a bunch of outfits dealing in the old manuals.