We've found that the kicker is quite important, some worked better than others myself favouring that vanilla scented stuff...Zip Kicker, that comes in a brown bottle or aerosol.
The foamex itself can be cut very easily and sanded to quite a good finish, one downfall is that sometimes it can be prone to shock if used in very cold water, smack something hard and you can have some excitement you hadnt planned on if its cold outside.
Most boats offered as free plans like 'Pug the Tug' or HMS Brush etc would be simple to build using foamex, just remember to ad some extra corner/edge bracing, sealing prop or rudder tube entries is easily done with 'metal' type epoxies, or if not available use quick setting type again mixed with a little Bicarb to thicken it up a little
One of our handicapped guest boat projects was built using foamex, cheap, easy to use and work on and stands up to those little accidents that they sometimes receive.
Paint also sticks a little better after a polish with a fine foam sanding pad or scotch type pad.
Have a look at our green barge being repaired on my webaite at
www.badbillsboatyard.co.uk to see how big you can go....Oh sorry, you can go 'MUCH' bigger as we also built a 6ft tanker for towing that bolts together, pics of that are on the scottish fedration website somewhere.
Cant find that Crane Barge article though?