I can't believe how many people are suggesting an annie for a truck gun for gopher hunting. I mean, cumon... really???
If it's for the odd gopher here and there get yourself something like a savage mark ii in stainless with a polymer stock on it, that will be truck-proof and won't rust etc.. throw a simply little 4x scope on there and load it up with CCI quiet-22 segmented hollow points.
If you really wanna take on a gopher army, then get a ruger 10/22 SS with a polymer stock, a 110 rd drum magazine and get the dlask charging handle kit with the spring for subsonic ammo in it, throw a semi decent red dot scope on there and load it up with CCI quiet 22 segmented hollow points.
You can even go for the takedown version with the little waterproof backpack to keep it in, avoids the rough and tumble of the back of the truck