What size rv cover?

I found it useful to have some room in the front so I can cover the entire A-Frame. I put a grommet in it and use a bungee cord to secure it the a point underneath.

I use a Sunshield tarp that covers the roof and parts of the sides, front and back. The bigger the tarp the more of the sides it covers. Check the weight of any cover you plan to buy.

FWIW, ADCO has introduced a new series called Storage Lot Covers which are a lot less costly than the AquaShed or Tyvek Designer series covers. These storage lot covers are much simpler, 4-layer polypropylene with no zippers on the curb side. I've owned both AquaShed and Tyvek versions, this winter I think I might try one of these new much more cost effective storage lot covers. In the OP's size ADCO part #74846 would get him a cover rated for 31'7" to 34'.

I agree with the size the other poster mentioned. If your box size is in ADCO's range, it will fit, even with ladder.
If you are getting an ADCO cover, make sure you get the "all climate with "Tyvec" roof. My first cover was an ADCO "moderate climate" designer series and the top fell apart after 2 winters. ADCO honored the full price since within the 2 yr warranty and I upgraded to the All climate one with tyvec roof. ...I just paid the $100 difference. The climate and winds in NJ I thought were "moderate" but the sun just disintegrated the top on the original cover in less than 2 years. This new one has a much tougher top and seems to be holding up better! Pay the $350 upfront and hopefully get 3 yrs or better the first time!

Thank you!

My 5th wheel is 27 feet of box plus a ladder too. I ordered the 27 foot cover and it fit fine. Plenty of slack to cover ladder plus spare tire.
Would recommend that you get some swim noodles or semi rigid pipe insulation. I covered the ladder as the sharp corners of the outer edge of the ladder would have caused tears in the cover. Also used at sharp places like folding steps, corners and rear bumper ends. Don't forget to get wheel covers too, to protect tires, as cover will not reach all the way to ground. :)