I use the lens with a Manfrotto Element Traveller tripod. Even though I have the impression that it is too small, I have had no negative experiences. I'm glad I don't have to lug around a big and heavy tripod.
I use the Mantona Gimbal KII as a head. That is also great.

Regarding rain protection, check out the Raincoat from LensCoat. They should be of good quality.

A backpack is one thing. What else do you need to have room for? I have the Lowepro Flipside 400 AW. There's simply no room for anything else. If I need more, I have a large outdoor backpack with the Shimoda Core Unit Large inside. The large photo backpacks are quite expensive.

I hope I have been able to help a little.

I use a Manfrotto Carbon 055CXPRO4 with ball head as a tripod.

This question has not yet arisen for me. First use in the last 3 weeks in Zambia, no rain, but dust ;-).

Still forgotten but a backpack which has good space for this size of lens