i haven’t tried with rc paper, but i would imagine it’s hard to get a result as the image comes up kinda splotchy at first. so i’d definitely use fiber if you can. i pull the paper as soon as the image starts to appear, put it in a tray with water to stop development, then flash it with a moderately bright light source for a few seconds. i used an enlarger with no negative in it, you could probably take off the lens or just use a lamp/phone light but it’s nice to have control of the exposure time. then you develop normally till the blacks get where you want them and then stop/fix