I use the sections they sell at the local car spares with metal ends attached, you can get various lengths and sizes to fit over your existing pipe and are easy to fit as long as your pipe is fairly sound. They are not expensive for what they do, last one I bought was about £8.
With the ready made sections you can also buy them oversize and cut slots then use a clamp to hold them in so no welding is required if you are not confident.
The trick to welding this stuff is to use a metal ring over the end, over the braid. Then it can be welded quite easily. The ring prevents the thing strip of the strip wound hose blowing through and gives a more subtantial end to weld to. Ring should be about 15 to 20mm long x 1.5 to 2 mm thick.
removed exhaust, cut the braided wire off which was a mission in itself. evil stuff.
done some cutting and lots of grinding and welded it up. hated every minute of it.
start stop start stop start......bzzt bzzt bzzt bzzt done my head in by the time i finished. especially when i was just stacking up little boogies rather than just weld the tiny hole i was aiming for LOL
after i cut it off, i fitted it all back onto the car, market it out so i knew what position to weld it, removed back off car, welded it up, fitted back on.....half an inch out
sounds much better now tho, and ive saved myself £60 so im happy.
now sitting down picking black sticky snobs out of my nose after all the grinding.