Class V hitch is Wt carrying -500 tongue wt , 5000 trailer wt
18" extention like Reese is rated to 350 tongue , 3500 trailer
If you can live within those weights thats a good length , wont drag to much if at all, just make sure you add safty chains to reach the truck . I have towed lots of boats to 18 ft bass boats like that and a 6x10 enclosed cargo also , all under 3500lbs . Good combo for campers to 9 1/2 to 10 foot
It says these weights right on the extention , Legal
If you make your own it dosent , not legal
But Ive also had superhitch for longer campers and higher weight trailers , the best
But they will drag if you get longer than a foot and a half or so depending on the drop of the reciver you use, superhitch makes a roller wheel if you drag , mostly Ive draged going into gas stations and stores going over raised and lowered sidewalks and such
Camper wise , I find that a camper under 9 1/2 to 10 ft is not big enough for a reasonable layout , decent size bath ....
Given that I did have 8 " campers w/no bath years ago and thought that was heaven at the time
I think a 10" camper is real a real good length to tow with
You didnt ask but brakes on the trailer make life and safty better with a truck camper , surge or electric