I guess....I can comment here....my Dump has a gooseneck hitch in the bed..
The is the truck, 1993 International 4300 "Low Profile", 5 spd, 7.3 IDI
This truck started life as a flat bed dump for a lumber company, the previous owner purchased it, added the sides, added a pintle hitch on the back, and added a goose neck in the bed.
Although I have yet hook my gooseneck up to this truck (I'm over CDL requirements if I do, and I don't have a CDL), I see no issues running a goose with the hitch set up it has in the bed.
As far as the other suggestion about welding the hitch to the frame and a trap door in the bed.......great idea, except on a dump truck of this size the sisscor lift will always be in the way and will not be able to span across the frame rails to mount the hitch....that's why mine is mounted in the bed.
This is about the best pic I have right now of the hitch, it's a simple flip up ball hitch that was welded and re-enforced in the bed, real simple to do, if you are afraid of the hitch ripping the bed, just re-enforce it more.
You can see where the hitch is by where the safety u-bolts are.
The moral of the story is....you need to find a "Low Profile" truck, with out the lower frame of my truck there would be no way that my jacks on my goose would extend enough for me to get the goose into the bed and hook up the trailer. As far as I know, International is the only one to make these types of trucks.
And even though the IDI does an ok job....fine one with a DT444e, or a DT466e (these are uncommon in the Low Pro), but with a DT444e you'll be familar with it.
BTW, I paid 6k for this truck....awesome little truck for the price, you should be able to find these all day long like this.