[doughboy]

The rim won't be damaged by the tyre being completely flat.

You need a jack with tyre weld as you have to rotate the tyre so the puncture is at the bottom, and remove the nail etc. This is very difficuly without a jack. (and chocks so you can take off the handbrake if its a rear puncture) (bmw jack comes with a wheel chock.)

You don't remove the valve, otherwise the tyre weld won't stay in.

I used it on a motorbike years ago (as they don't have spares either!!), worked fine, no valve removal, just squirted it straight in and span the wheel round as I didn't know where the puncture was!

Pumped it up a bit more at the next garage.

As you have tyreweld, the instructions are on the can!!!