Rack can be mounted with stock grab handles, or without them. If stock grab handles are removed, additional spacers (provided with each rack) or model specific Subplate(purchased separatly) are used. Rotopax canisters can be fitted in all three variants.
Instruction details can be found here. It is worth mentioning that Rotopax canister can be mounted in two positions, more towards the front or more towards the back.
Position 1, more to the back.
And position 2, more towards the front.
Here are few photos of Rotopax 1 gallon can, mounted in Position 2, with stock grab handles. Front and rear slots are accessible, so something can be strapped on top of Rotopax, if needed.
And here are few photos of Rotopax 1 gallon can, mounted in Position 1, without stock grab handles. Top luggage rack is mounted using the Subplate.