Your Sport is so short, it may not even reach a bed (cargo) extender, so there wouldn't be much support there, if any. Notice the red Sport in this pic (top right) -- it stops just about at the extender and is not all the way forward:

There is a simple solution. Here is a Revo 11 on a 6' bed:

Notice with the tail gate down it is fully supported by the truck bed. Your Sport is 2' shorter and would ride very similarly in your 5' bed with tailgate down. Perhaps you're concerned about it falling out the back? That's not a problem -- I drive mine up a 14% grade every time it goes out. Notice on the picture above, the rope is secured to the tail gate cable on the right. Loop it over the scupper cart twice and tie off on the opposite cable (note -- you should not do this if you don't have the reinforced scuppers -- they have a black liner in them). Tie down firm enough so the stern doesn't slide around. That's it. If you don't feel comfortable with that, you can use your rear cargo tie downs and loop your rope through the scupper holes and/or loop it around the rudder mount. For double extra safety you can clip the bow to the nearest front cargo tie down. Because the boat sits diagonal in the bed, it doesn't stick out as far, and the bow is pinched in one corner so it can't move.
How hard is it to load? You don't have to lift the boat, as shown below:
1. Roll the boat up to the lowered tailgate and set the bow on it.

2. Lift the stern, letting your wheels drop out of the scuppers.

3. Push, positioning the bow in the corner and the wheels upside down in the scuppers, and tie off.

Edit: I just found a shot of a pair of Sports for comparison on a 6' bed. Notice how the tip boat is tied off, double looped around the cart axle and separately secured at the stern and bow.
