I did this with my 2017 Ridgeline and a KTM 790 Adventure R.
Definitely pushing the limits of the hitch and the lift hardware, but it was all within bounds and never had any issue with it once you get used to it swaying a bit with bumps and turns.
Haven't tried yet on the Rivian but I'm...
Tech told us water gets in the horn, which is why it sounds silly generally. Imagine this get exacerbated by cold conditions.
Can blow it out with compressed air, he said — assuming its not frozen.