I use Mousse from time to time for enduro but I will not recommend it for traveling.
If you want it to last you will have to lube it regularly so in the end it will be more hassle then running a tube and fix the occasional flat.

Lubing is not a problem in enduro because the tires only last 10 hours anyway... But personally I don't use mouse unless it's very important not to get a flat. Mousse is a lot of work and it's not possible (or at least not easy) to play around with pressure. It protects the rim a bit better then a tube.
HD/UHD-tubes works pretty good.

Mousse is very expensive.

A trick is to use mousse for larger wheel dimensions, this will increase "pressure" and it lasts longer - but it's even harder to mount.

25 years ago when I was driving trial I used the old tires on various bikes. It was far from perfect, they didn't last long and they didn't like wet conditions (rain/mud) or sand. Last year I tried a Dunlop 908 on my GS and had to limp home after 250kms...
My guess is that Mitas MC-18 is a far better choice and it works very well in mud. I use it for Enduro and will probably give it a try on the BMW, and hopefully it will last a weeks expedition...

BTW (and back to topic):
I have run tubeless 0.5 bar (7.5 PSI) on a heavy bike without problems for rather long distances.
The last years I've increased pressure (to save the rims) and kept higher speed. It works.