Can the trailer valet be used on slopes or inclines? 

The trailer valet can only be used on hard paved surfaces with slopes of 7 degrees or less. 

The following link will take you to a video that discusses this in more detail. 

https://www.youtube.com/watch?v=SmoUXVw05Y0

Is the Trailer Valet suitable for a D035 Hitch?

How to install your Trailer Valet 

https://youtu.be/-yuaedrpNas

How to install your Trailer Valet Mounting Bracket

https://youtu.be/TnGLLYe_Uog

Instruction Manual for Trailer Valet X5

https://www.campsmart.net.au/assets/brochures/42965.pdf

Instruction Manual for Trailer Valet XL

https://www.campsmart.net.au/assets/brochures/43705.pdf