To fully cope with the requirements of innovative 5G use cases, evolving business models and flexible networking scenarios spanning multiple administrative domains are envisioned. In this context, transparent and trusted frameworks that enable network service providers and infrastructure providers to advertise, negotiate and acquire, in real time, 5G resources and services, distributed over various geographical areas, are extremely valuable. To address this goal, emerging Distributed Ledger Technologies (DLTs) arise as well-suited solutions to ensure distributed security and trust, as well as effective and agile transaction management across the various parties involved in the 5G service chain implementation. Following this vision, this paper presents the design of a DLT-enabled Marketplace aimed to foster the secure trading of heterogeneous resources in dynamic 5G ecosystems. The performance of an initial implementation as proof-of-concept is also analyzed. The results of this proof-of-concept validate the feasibility of a decentralized marketplace implementation in the context of 5G resource trading.