Welcome, SalidaC! Not sure if you are thinking of the whole futon slide out to a bed thing, or just the cushion. If I remember in our 179 the plywood on the seat base was pretty thin and may well not support a futon frame extended. I know we're supposed to be able to make a bed with the foot rests (which we removed) but just not sure. Keep in mind you'll want room to pass thru and to open the bathroom door enough.The cushion idea is good if it'll fit lengthwise. The cushion provided by the factory is too thin to sit on comfortably for any length of time. Measure twice, experiment, have fun!
Greg 'n Deb
2020 R-POD 195 HRE
'17 Tacoma 3.5L,'07 Tundra 5.7L w/ tow pkgs.