The Vendor will have a good idea of what is required for infrastructure and should be asked to produce a specification for the solution. This can be discussed and reviewed internally. The results of the Technical Trial will also identify requirements for infrastructure. Even if there is no cost involved, the item should be included. This document will form part of the planning for implementation.
At the end of the process, an Infrastructure Requirements List should be produced which also contains costings. If a number of solutions are still being considered, the infrastructure requirements will have to address those options.
There is potentially overlap with the work in developing an Implementation Activity List. You will need to ensure that the two lists are compared and overlaps/under laps are resolved.