Mounting for rear rack

[Dr pepper]

My bicycle has a tubular cross mount for the rear brake instead of a flat plate brazed or spotted on.
My rack kit comes with a 'U' bracket that is meant to bolt onto the rear brake hole, I carry up to 10kg or so would this be a good idea?, or should I fabricate something that secures to the seatpost.
The rack of course also bolts to the dropouts.

 

[fossyant]

Should be fine as the weight is supported by the drop outs. For a seat post mount, I've used old light brackets a few times.

The brake mount being tubular is pretty standard, flat ones tend to be on cheap bikes. All depends if the bolts are recessed and you've enough thread available with the rear rack mount.

 

[88robb]

My bicycle has a tubular cross mount for the rear brake instead of a flat plate brazed or spotted on.
My rack kit comes with a 'U' bracket that is meant to bolt onto the rear brake hole, I carry up to 10kg or so would this be a good idea?, or should I fabricate something that secures to the seatpost.
The rack of course also bolts to the dropouts.

Using the 'U' bracket on the brake mount is the stronger, intended method. It's designed to handle that weight. A seatpost mount is less stable and can slip or sway, especially with 10kg. Go with the brake mount bracket.