In my experience you get what you pay for. The stand-alone apps that are commonly used usually don't allow you to enter the vehicle parameters, which makes the routes useless for a motor home unless you're in a small class B.
There are a few paid apps I've tried, and none give me the functionality of the Garmin. True, the Garmin is not perfect so no need to remind me of that. But, in all the years I've used GPS units and the various apps it's still the best I've found.
All that said, here's one online app I've just found which allows you to view weather on your route: https://morecast.com/en/plan-your-route