Just an update from my previous post re this issue.
At long last we have sourced a portable DVD player from Curry's with the required AV IN socket. With suitable cables its a simple job to plug the thermal into the screen, from last nights trial we were very impressed by the picture quality and its very much easier to now scan out oF the truck with the remote screen. We need to resolve issue of screen brightness which is quite bright so needs reducing, may do this through image brigtness on thermal, but will have a play.
Will need to rig up a dash board mounted cradle for prolonged use.
Two DVD players were £100 from Currys. Will post exact model later as not readily to hand.