Welcome to iRV2.
I think you would be close , adding 8' as an approximation. BUT!
There is some discrepancy within the industry as to where the actual measurements are taken, on 5ers in particular.
Some include the length of the front to the cap and the back bumper.
Others go from the front of the pin box to the back edge of the RV and don't include the bumper.
My last 5er, sold as 27'6" measured 30'
. Even the living space inside measured over 27'6".
The optimum placement for a 5er hitch , is for the center of the pin to be 2" ahead of the centerline of the truck's rear axle, so the only way to get an accurate length of your overall vehicle , would be to know the distance from that point to the front of the truck , and measure the 5er from the pin to the rear bumper.
Good Luck in your search , hope you don't find this info confusing.