Striping underseal ,do i .....
 

Do I have to take the carpet and seats out , I've heard the heat from grinding the paint back on the outside could cause things on the inside to melt

Depends how you do it. If you look at my project thread i mainly used a 115mm steel brush on an angle grinder. Very horrible job and you have to try to all the get all the under shield and the paint (if you want to go that far down to bare metal) but stop before you burnish the metal otherwise it will be so shiny nothing will stick to it. You can used sanding discs on a grinder but they clog in no time and it would cost a fortune.

If you use a wire brush make sure you wear goggles, thick leather gloves and ideally full face protection. If you get hit by a bristle it is very likely to stick in your skin. Also they end up everywhere so prepare for that too.

I used a scraper to get the old seam sealer out manually with the help of a heat gun and then a dremel for bits I couldn't get the grinder in. Also be careful of loose fabric with the grinder and for when it latches onto something and tries to rip your hand off.

As for heating the metal. Yes it make it very hot. Some parts of the car you could get away with doing without taking stuff off but I wouldn't be doing anything where there is carpet, wiring or fuel lines behind it as it will melt things or even light the sound deadening. My shell was bare so safe.

Be very careful.

Thanks for the heads up lloyd , I spent today stripping the interior out the car , I'll make sure and keep the wires up out the way and I think having a fire extinguisher close by might be a good idea

Try dry ice mixed with some IPA. It can make the underseal brittle and much easier to remove :)