I attached pictures that have all of the dimensions for the RearView Safety Flush Mount Bracket # RVS-421 that you referenced. Overall it's 7.875 inches wide and 6.125 inches tall. view full answer...
According to the floor plan, for options 113, 131, 208, 833, for your 2018 Holiday Rambler Vacationer 35P, then you have a King Eurotop measuring 72" x 75".
With that information, the etrailer eDream RV Mattress # e64FR is the correct size replacement for your Rambler. view full answer...
I wasn't quite sure the exact measurement you were referring to in regards to "diameter of the rim alignment ledge" for the Trailer Idler Hub Assembly for 2,000-lb Axles # AKIHUB-440-2-2K so I took a number of measurements of this hub.
If you take a look at the accompanying photo I made you can see each of the measurements. I have also added a link to a video review of this hub for you to take a look at as well. view full answer...