I would not use the welders at Grenada Marine. They were an absolute disaster for us when trying to close a thru-hull on our previous
aluminum boat. They did very sloppy and ill informed MIG work (for example, not using a clean ground clamp to the hull, and so constantly losing the
arc mid-weld). I tested the weld with soapy
water and compressed air the next day, and bubbles came through all along the new weld. I asked the yard manager to either find a different welder or have this one more carefully supervised (and taught) by the metal shop manager, and he became very aggressive and threatened to stop all work and leave us stranded in the yard. I'm a very mellow guy, I've been dealing with yards all over the world for twenty years, and that's the only time I've had someone explode or threaten me. The welder lied and claimed we hit it with a hammer on the inside of the hull while he was welding, disturbing the puddle. Just weird, and so much drama. Some people like their stainless work for arches (and etc), but as a hobbyist welder, I was unimpressed by the way they 'cheated' (using TIG on a low amp pulse setting with no filler rod) to make good looking (to the uninformed), but weak, welds. That said, I was happy with their carpentry and painting departments.
Nick at Technik (Spice Island Marine) is good, but he is very busy. It took him months to get to a small job we had.
I feel your best option is the yard at Carriacou. The yard is small, inexpensive, low key, and friendly. The gentleman who welds, who has his own shop on a big converted
trimaran, is very good. However, you may want to contact him before you go up there, to see if you need to bring whatever metal with you. When I was there he wanted to order raw materials from
Martinique, which is slow.
The best situation I know of is in
St Martin, if you can make it up there. We had excellent work done there.