I'm sorry but I have no suggestions for the website you're looking for and hope someone else can come up with an answer to your question.
For years I've been using Microsoft Streets & Trips software for planning RV trips and delivery routes for my Lions Club citrus sales. In recent years I've been transferring that data to my Garmin using gpx files. It works quite will for the citrus routes (where the delivery points are close together) but not so good for long trips unless you put in a lot of extra waypoints in before uploading the gpx file. Garmin will reroute as it sees fit between waypoints which may or may not be the way you want to go. I can only assume that this would be the same with any other mapping software gpx uploaded to a Garmin.
Since Microsoft last updated S&T was 2013 and there will be no more I’m like you and will have to find some other trip planning software also.
Dave