Yes, I used to be on the committee of the NW GSP club so I am familiar with all HPR breeds, in particular GSPs. I have no experience of such grumpiness, but have probably been around fewer Weimaraners than of any other HPR breed. My intact males and bitches could be put in the trailer with any dog and never had an issue. That’s not to say they don’t have it in their locker. In Europe they were traditionally used for guarding as well so that may be part of it. My pregnant wife and her elderly aunt were on the beach with me in north Scotland. A badly trained Labrador attacked my wife (jumped up at her) and knocked over her aunt. As I was carrying my toddler son I instructed my dog to “Get On” and he savaged the Labrador, the size and power difference between the breeds was evident as was the steeliness. I had to quickly call my boy off to avoid the Labrador being killed, my bitch stayed to heel.