Good advice on smaller camper. Camping spots get filled up quickly. Lots of times, you need to call ahead and reserve. There are still options to just pull over and sleep but not like my college days back in the 90’s. Lots of access areas closed off.
If going for the fishing - go to ADF&G and check the weir counts for rivers you are thinking of fishing. AK fisheries management is terrible and they are slowly killing alot of the runs. Some accessible rivers besides Kenai (def need a guide on some of these) - Gulkana and Klutina in summer for Kings, Deshka, Susitna for silvers in the fall.
Can head to Seward, Whittier, or Homer for Halibut for offshore silvers and kings depending on time of year.
If you have the time and are up for an adventure, look at leaving your rig at Homer, Whittier, Valdez, grab your tent and bags and hop on the Alaska Ferry and hit up Southeast Alaska. You can buy rooms to sleep on ferry or they used to just let you pitch your tent on deck back in the day. Southeast is pretty cool.
Have fun!