If you build 'plank on frame', it depends on whether you wish to keep detail of the planking, I didn't use resin on the outside of my trawler hull, as it is 'carvel or flush planked' & a fine sand plus 4 coats (thin) of Humbrol enamel gave it a good seal.
However, if you are planking in the 'clinker' style, you wouldn't want to detract from the effect by using resin on the outside either.
These are just my views, I'm quite new to this hobby, so err to the more experienced on here.
Edited By Kip Woods on 26/11/2014 17:56:04