Yes. The Classic Accessories Deluxe PolyPro III Heavy-Duty Cover for Class B RVs - Up to 20' Long # CA80103 will fit your 2018 Roadtrek Simplicity Motorhome that is 19 feet and 7 inches long.
It will fit on class B motorhomes with dimensions up to 20 ft. long x 84 inches wide x 117 inches tall. view full answer...
The CE Smith trailer hub assembly part # CE13511 will work for you and yes you could reuse the dust cap you have now that has the rubber plug for access to the zerk fitting. Or you could just cover up the zerk fitting with the included cover as well. view full answer...