Glad I'm hearing this conversation now. I'm fixing my flatbed and I'm installing some bracing under it to accept a gooseneck ball and / or a fifth wheel mount.
When my truck is complete, I was planning on taking it to the local scales and measuring the weight on the front and the weight on the rear. I know my maximum front and rear axle weight. Based upon that I can determine the total load weight I can put on the hitch. I can then take this max hitch weight and use it to determine where the hitch should sit to distribute this weight between the two axles. I've been told by many people it'll be about 4 - 6 inches in front of the rear axle.
I have a question about the 5'th wheel hitches. How do they connect to the truck bed? I'm assuming some bolts, but what are the dimensions of the attachment surface?
Thanks.