When did slide outs first show up?

For the RV industry, manual slide outs with manual slide out frame supports began in the early 1980's (mainly on large park model trailers). Tip outs, as shown in your picture showed up in the mid 70's. Electric slides arrived in the late 80's early 90's in class A motor homes and then in travel trailers in the mid 90's .... slides have evolved and improved over the years, our trailer has opposing slides that open up the entire center of or trailer for that residential feel.

Lou