More carrying suggestions...

I need to put a tent, sleeping bag and roll mat on the back of the
bike.

Take the car.

Not much cop for a motorcycle tour though.

You know what? I look at some pictures of that after you posted and
thought "I quite like that".

Maybe in ten years.

Bear in mind, I have twin underseat cans with no heat shielding and
they stick out a little from under the seat.

Renntec sportrack with everything bungied (or similar) on?

Pillion seat, tail pack, bungees.

You'll die, mind.

Lord knows I did,

I did an indicated 160 on a bike with both D207Rs and a tailpack fitted.

Died instantly, of course.

We laugh because it's funny, and we laugh because we wish it were true.

August 3rd Camping Magazine [1] will have a feature on Camping by Bike
[1] don't ask

I'll make a note to get the issue.

Though I doubt they'll be "Camping by ZX10R".

it'll probably say strap it to the handlebars.

ventura luggage system?

looks a bit pricey

I guess it is - though it's cheaper and more appropriate for a sports-
bike than hard luggage.

Thinking about it, for a sprotbike, a rack with side rails which could mount
a pair of monster size soft panniers would work quite well.
One might want the natty sprotbike ally subframe copied in steel first mind.

Are you suggesting you don't want to bungee stuff to the pillion pad?
If you are happy to do so then one of the big Oxford roll bags, or similar
alternatives, will hold a tent, bag and matt with a few clothes easily
enough. Mine is pretty waterproof. Bonners was promoting something similar
recently if you web-search.

I've not used the system myself but a mate rates it highly. He's used it on
a variety of bikes.

Rather pricey IMV.