1990's Chevy RV chassis is either P-series (shared with step van) or G-series (based on second generation Chevy van). If over 12,300 pounds GVWR, it is almost certainly P-series, so that's where you start looking for parts.
Commercial applications for these chassis greatly outnumbered RV production, so go into the parts store with the idea that you have a General Motors P-30. If you can find the chassis VIN, the model number from that will help trim down what has to be searched. There are tens of thousands of bread vans and potato chip vans sharing parts with you.