Check out Bettablast.co.uk in the blast section they have all the different blasting media shown, I'm sure Bill would give a quick reply as to which one would do the Trimble. He's really helpful and has done some impressive work e.g. Donald Campbells Hydroplane.
I'm used to this problem for lightweight sailing racing dinghies. Nitromors is too aggressive - it can be used but you have to be very fast. There is another formulation for stripping GRP, but it's not so good.
I would only recommend stripping if the base cost has failed and it's peeling. Otherwise a gentle rub down to key it nor the new coat is fine.
Usually most damage to GRP is done by breaking the outer gel coat. The glass fibres absorb moisture from the air and it all then weakens the structure.