The contracts themselves, in the form they will actually operate. Each shipyard agreement should show deliverables owed by the American subsidiary, acceptance criteria, and the subsidiary's own manager directing and supervising Félix, supported by an itinerary of the work and the reporting arrangements.
Offsite placement is proved by the contract and the reporting line
A specialised-knowledge beneficiary placed primarily at another company's worksite has to clear two additional requirements, and both are documentary before they are factual. The first is that the petitioner controls and supervises the work, which is evidenced by naming the supervising manager, describing how instructions reach Félix, how his output is reviewed, and who appraises him. The second is that the arrangement is not essentially one to provide labour for hire, which is evidenced by scopes of work defined as outcomes rather than as a body on site, by pricing tied to those outcomes, and by the employer supplying the methodology and tooling.
Alongside the contracts, an itinerary setting out the anticipated dates and locations of the work should be filed, because assignments spread across three yards invite exactly that question. If a yard has already begun treating him as part of its crew, correcting that before filing is more useful than describing it accurately afterwards.