Since your overall length is 17' 10" you may be OK with the 15' 1" to 18' size. It is already going to be a little bit big because it is made to cover up to 8' in width and the SLX 7 line is just over 7' wide. You do want it to fit fairly snug so that it doesn't get torn up from flapping in the wind. You also want to cover any sharp objects such as the gutter extensions to avoid holes from the stress points.
TT: 2019 ORV Timber Ridge 23DBS, Blue Ox SwayPro 15K/1500
TV: 2019 Ford F-250 XLT SuperCab LB, 6.2L, 4.30/e-locker, 4x4, 164" WB, 3216 payload
TV: 2014 RAM 1500 Big Horn CC (Traded in)
TT: 2015 Jay Flight SLX 195RB Baja Edition, Andersen No-Sway (Traded in)