Hello...
For a 'truck gun', I see nothing wrong with a Mini 14. It all depends on what you want out of your rifle. If you are looking for pin-point MOA accuracy at ranges of 100 yards plus, a Mini does not have it. If you want acceptable accuracy at shorter ranges, then you may be in the ball park. My Mini 14, which is a dated model now, shows best accuracy at 100 yards with handloads. It has enough accuracy to shoot chucks at that range, and I think it would be an excellent all-round truck gun. A friend advises to get a Stag Arms AR in .223, however. I have no experience with a Saiga, so I can't comment.
Once again, it depends on what you want your rifle to do. If you are looking for superior accuracy, a Mini 14 does not deliver the bacon. For reliability, fast handling, and access to a world of accesories and add-ons, there is nothing wrong with a Mini.
Cheers,
Gary