The MDF sheets are all glued and screwed together, all edges/surfaces planed flush then sanded, before filling all gaps with polyfilla. After sanding, smooth finishing using polyfilla and final sanding the surface is smooth, and the butted edges of MDF are all flush. Then after hoovering off any dust ( i didn't want to risk a damp cloth and raise up the surface), cut out the fablon about 30mm oversized and carefully apply.
To get the clean corners I used a brand new Stanley blade to cut the fablon, gently running the ground edge along the adjoining face of the sub at about a 60° angle. I only managed to nick the previous pieces a couple of times overall and if you take it slow these can be stuck back down before coming fully detached- start at the back to get confident with it.
Around the recess for the speaker i did exactly the same, running a thin strip of fablon along the inside face. This came away in places so i used some superglue to re-attach it. Looked spot on so far. So then I ruined it by catching the fablon on the chuck of my drill as I did the pilot holes for the speaker screws!! Not even just the once but three out of the eight holes
Still looks the part mind, though next time I think veneer will be the way to go.