If the ‘basic gun’ you mentioned is the heavy cannon, that thing is extremely useful in campaign 4: desolate hills, especially if you use all its points on just damage ups, and put it in turret position 2 while filling the rest with those passive defence barricades.
I’m not sure what you mean by no save feature between campaigns on StormWinds. The game DOES save automatically in between every single wave as well as in between campaigns.
 "ZarionBloodwind"){kind=small}
 "HeroInteractive"){kind=small}
 "magicmarc"){kind=small}