First, you need to be specific which boat to include weight, width and depth of keel. Next, please do not tell me you are converting a power boat trailer as I will stop right here. Do you have any experience building trailers? Bill Roosa also brought up good points. I was a sailboat dealer who designed sailboat trailers for myself and some for specific models as I learned from a good friend who designed sailboat trailers for a living.
You will need a tandem axle trailer with brakes heavy duty of course dealing with a 5 ton boat which will require a strong keel tray, tractor trailer style tires,four uprights each side to support the boat hull and a forward bow support upright as well and so forth.. You will need an extension, not a strap contrary to some would say is safe as you would be at the maximum weight for a strap with no safety factor built in. You will need a crane or something like that to remove the mast every time you transport and need to know how to tie it down with cushioning material. You will need a spare tire or two. You will need to know the ramps which to launch from as most you will not be able to do so. You will need to know the laws of each state regarding the time of day and when if the boat exceeds each state's width laws as you will need permits for each state. The list goes on.
Most who transport large boats also have a dooley with diesel engine and so on. An F150 will not do particularly going over mountains. Those who did on a regualar basis had a professional trailer built by those who know how to.
Am I being tough on you. You bet so. I have seen the after math of many accidents with boat trailers and the failures of those which were home built. How much experience I do have. I use to launch up to 34 footers with mast up with a crane over a bridge safely. This is something where safety is a must when dealing with heavy displacement boats and at 5 tons, that would be in this category.
Now you are beginning to question me. I have the experience and most do not but safety is very important to me and I cringe when I saw your post.