i'm assuming you'll be covering balsa or ply. if so, then you can use aluminum tape but you will still need to 'glass the balsa to get a smooth surface as the tape will show any and all imperfections in the balsa surface. i would go this route. to get the crisp edge you want, remove the cowl and tape any other edges that you don't want the epoxy or polyester to get to. then, after the 'glass/epoxy has cured sand the excess fiber from the taped edges to give you that clean edge. it will be much easier to smooth the 'glass around a compound curve than most other methods mentioned. also, the aluminum tape will also form to a compound curve with patience and practice. of course, using 'glass/epoxy will negate the need for the alum tape unless you want the look of unpainted metal or you want some wx'ing effects.

i did something very similar on my Fairey Flycatcher except i didn't mask the edges as i didn't need the clean edge prior to covering with Solartex. here's the link to my RCU thead showing what i did: http://www.rcuniverse.com/forum/m_14..._2/key_/tm.htm

hope this helps some.