Making my own trim from MDF. 1/4 sheet sanding is taking too long. How to speed up sanding edges in bulk? Will oscilating edge/belt spindle sander speed up? or too rough sanding?

So we have been making our own trim recently from 3/4" 4'x8' sheets of MDF. We did one room with MDF wainscotting, and it turned out really good. Our process is : Cut strip > 150 grit sand edges > prime with Zinsser Shellac primer > 220 grit sand > Paint​The problem is we then have 12-13 strips which are 8' long and need the sides to be sanded smooth. This takes FOREVER. We want to speed up these edges. We are DIY'ing so would prefer the money savings over pine, but dont mind investing in equipment.​We saw the "Oscilating edge/belt spindle sander" for $250 and are considering this an option, however I feel like belt sanders are more for removing wood and not actually sanding it smooth. Whats the fastest way to sand the equivalent of probably 400-500' of edges? our 1/4 sheet sander isnt cutting it lol. via /r/DIY https://ift.tt/31q5DP3