I would find a floorplan that you like and start there. There are many similar floorplans in different lengths. One thing to remember is, older CG's were most probably built to handle RV's in the 30'area. That doesn't mean that you can't get your 40' 5er in there....it just means experience is helpful. Choose CG's with that in mind. The thing that concerns me more than length with a newbie towing is overloading the TV. I think that the pin weight on a 40', king bed, bunk house might be over the payload weight of a fully fueled, kid loaded....SRW. Check your weights!
