A couple other things to consider.
If you get the 40'er, if it has high enough ground clearance at the tail end, you often will be able to back some to most to maybe all of the trailer behind the rear axle past the parking curb, significantly increasing the number of campsites that it will fit in. Just make sure you have enough clearance behind the curb to allow for all that trailer before you hit a tree.
Longer trailers react slower when backing. This can be a good thing for a person new to backing/maneuvering a trailer as long as they don't overreact. Take you time practicing and getting familiar with how quickly the tail end comes around and how much space that takes.
As mentioned above, watch the tail swing out when you turn. A very high percentage of long trailers that are damaged by new drivers is due to this. Try to fuel and park places that you have plenty of space to pull past obstacles in a straight or very slight turn. BIG truck stops and gas stations with very large parking lots are you friend until you get comfortable with your rig. USE THEM!
Also as mentioned above but worth repeating, IF IN DOUBT>PARK AND GET OUT! Even with a second person watching for you, stopping, getting out and walking around the back of the trailer, taking in everything around you that you have to watch for but cant see from the drivers seat, saves accidents. and Don't forget to look overhead also. Tree Limbs, wires, etc can cause a lot of expensive to fix damage.
Good luck in getting the perfect rig for you and your family!
