Following these instructions, I now have a Raspberry Pi connected to an Adafruit 3.5" TFT display. The display has a fixed resolution of 480x320, which presents problems when viewing some fixed-sized windows (e.g. the Openbox Configuration Manager). I asked over in the Adafruit forum if there is a way to set up a virtual desktop screen size, and it looks like the answer is no.
I'd like to know if there is a window manager that could come close to simulating a virtual screen size larger than the fixed 480x320 that I currently have. What I have in mind is, for example, a 2x2 array of desktops in which the windows overhang into other desktops. LXDE and Openbox are easily available for the Raspberry Pi, as are others, I'm sure. I'm not wedded to any one window manager, but the best solution would be one that is lightweight.