Size does matter...:B:B::B..45' is not too long...that said, you will have to rethink your camping agenda. With a large rig, most of us like the creature comforts..i.e. full hookups, 50amp service etc. etc., so we don't do a lot of boondocking. Obviously the larger the rig, the larger the holding tanks etc. but...We've found our limit is about 5 days before our tanks are full. If you like State campgrounds your choice is somewhat limited. Check where you are most likely to go and see how many sites they have available for big rigs. With a small rig, you can just jump in and go...you'll fit almost anywhere..the 45' not so much.
As for the turning radius, check the unit you're considering closely. My tag lifts making the turning radius much less than if I leave it down. We went from a 27' Winnie to a 40' to a 45' and don't regret it for a minute. The extra 5' may not seem like much but it's huge. Same with the tag..driving it is a breeze. The tag provides more CCC but you sacrifice one storage compartment.
We stay off Interstates when possible and have been mostly on two lane roads and some single lane roads with no problems. I do scout the CG when we arrive to look over the road situation, mostly for my comfort zone. There have been very few CGs that I would not fit into. That said, those that I felt I couldn't fit into, I wouldn't want to anyway...:B:B....
My advice...drive a 40' tag and a 45' tag and see the difference. Also, check your State's drivers license regulations. Some States require a different classification for anything over 40'....Dennis