I made the mistake 13 years ago of believing those that posted that 36' was the longest for USFS CGs. Did not take long to learn that is not true so traded for a 40' single slide and then a 42' 4 slide... Even used each change costs $$$$. Built the MH bay big enough for a 45' ... Just in case but happy with what we have.
I now say... Buy more MH than you think you need, ONE TIME! Rarely do you hear from the owner of a BIG rig that you should buy something smaller. Not sure how the owner of a 30' knows where I can get my 42'. Yes, it has the scratches to prove it as we boondock often.