I'm sure most don't include the length of their tow vehicle so I'd go with 30' in your case. Worst case scenario you might need to park the TV at an overflow lot but usually you can find space on your site.
Mine's a 23' with a 4' rear slide. Provincial parks near me class midsize trailers as up to 25' so that's the number I usually go with and I've never had issues.
2007 Shamrock F19 hybrid - 2010 (22 nights), 2011 (24 nights), 2012 (11 nights)
2013 Surveyor Select 235RKS - 2012 (6 nights), 2013 (32 nights), 2014 (26 nights), 2015 (37 nights), 2016 (14 nights)