The now gone 33' Titanium had a rear cap and really looked nice. My fuel mileage was 12-13. The current 38' and heavier Montana doesn't and my fuel mileage is ta-da!! 12-13.
When I asked an honest (an oxymoron?) RV salesman why many premium 5ers no longer had the molded rear cap, his answer was money - the cost of manufacturing and the sell price, no other reason. Some do offer a rear cap at about a $2K adder which will, at current diesel prices, put 1000 gallons of fuel in the TVs tank, or figured at 13mpg, 13,000 miles
Ford F250 6.7 Lariat CCLB, 5er Hitch Option w/ Rite air bags,
Montana High Country 343RL (sold it!)