Anybody know of a builder prepared to fit out essentiall a bare fibreglass hull?  Only need to be relatively few control lines for river use?

usual suspects. I suspect laurie or Ian are your best bets if you are based in the Thames area. Laurie (Haywards Heath) West Sussex) Ian (Southampton)

See link for contact details.

Try Geoff O'Neil at The Welsh Harp Boat Centre. (Wembly) Very good and fair with cost.
If you talk to him tell him Rocket 0_1 has found a lifting for the champs.