We're NOT talking about a '36" extension' here either. Extensions are measured pin hole to pin hole, not overall length.
This is a 9.5' camper on a long bed truck. An 18" extension should be adequate unless this boat trailer has an extremely short tongue. If the tongue goes under the camper a little bit, that's okay. What matters is the boat doesn't hit when you go around the sharpest corner.
https://www.etrailer.com/Hitch-Adapters/Draw-Tite/HE18.html
Just be aware that the extensions are VERY limited. 350lbs tongue, 3500lbs trailer.
If you want/need more the price is going to go up.
