This paper focuses on the relay antenna selection problem in a Vehicle-to-Vehicle (V2V) communication system employing physical layer network coding (PLNC) with amplify-and-forward (AF) scheme over double-Nakagami-m fading channels. We obtain lower and upper bounds of end-to-end signal-to-noise ratio (E2E-SNR) and their cumulative density functions (CDF). Employing the CDFs, the performance of the system is evaluated in terms of outage probabilities. We analize asymptotic diversity order of the system and express it as a function of number of relay antenna and channels parameters. Finally the analytical results are verified by the simulations.