@Ahmed.
I used cementx (same thing like samad bond but much stronger) and I never feel any trouble to remove samad bond, I used this on may other places in my previous cars and when ever i want to remove, it removed very easily. just a little quantity of petrol and kerosine oil required. About moisture, Jambolon is water proof, so lets see what will happen
Why you need to cover the Bonet? covering the bonet have two purposes as far as I know. 1- reduce the engine sound. 2- prevent the outer layer of paint from internal heat.
City has already a quite engine. and after a long run I never feel so much heat on outer side of bonet. but do give it a try, its your car and doing a harmless DIY wont cost much 
but I prefer if you can get a orignal insulation for this model it will be a gniune fit and durable. Using jombolon inside the bonet with samad bond hmmmm can cause some problem, both are vulnerable to fire etc. experts can guide better.
@ansar
YES, in this model of city interior is pathetic and doors starts making screething noises on bumps. now the driver side door is completely silent and its component's sound is much solid and different from all other 3 (other 3 doors are still remaining) I have double insulated the door, means first i insulate the inner side and then outer. I use pieces for inner side.
