No masking tape, it doesn’t seem to stain anything which is varnished but if the bass body was pale in colour I would’ve been careful not to get any on it.
All I did was lay the bass on two flat cushions with a strip of kitchen towel on top of the cushions, cleaned the fretboard with lighter fluid and a microfibre cloth, then caked on the Montypresso with a rag and rubbed it in. Made sure there was a really thick coat everywhere and left for 24 hours. The Montypresso is so thick in consistency that it didn’t drip or anything like that. So I now have a much nicer looking fretboard with no anger from the wife due to stained cushions/table etc.