What steps should i take to install my fat mat (dyamat)

[1970 TT Rustang]

I got a 70 mustang iam redoing the carpet and doing fat mat. The floors are in great shape no rust. Ive been told that por15 is great stuff to put down before hand. But i think its a little over kill, is there any other things i should consider before putting down the fat mat? Again i have no rust and solid pans. Should i keep the stock sound/ heat sheeting and lay the fatmat over it? Also how would you suggest i prep the area before laying it down?
Thanks
Rich

[overZealous1]

do not put over the factory pieces. the fat mat will be useless in those areas. it needs to be on the metal surface to deaden the vibration. doors and roof can usually use just one layer, floors typically get 2. use a hair dryer or heat gun to put it down. if it is cold, sometimes the adhesive will not stick properly. lay all the factory sound deadener and carpet deadener over the fat mat.
again, the fat mat works by absorbing vibration. it will take out alot of the higher pitched sounds, but very tough to stop the lows. if you are trying to conserve on material, you can concentrate on more of the flat large areas. compound curves or corners in the metal will not transmit the vibrations nearly as much as a large flat panel. to really have it make a big difference, you really have to do the entire cabin (especially the firewall and floor) and make sure to seal up any air gaps or holes.

[1970 TT Rustang]

Ok Thanks with the oem sound dedener do you think it worth putting it back in over the fat mat? Iam doing the fire wall floor and maybe the trunk. Do you think i should clean the floor pan and the firewall with any kind of soultion, or just a good vac will be good? i have 50sf of it so iam going to try to get everything done besides the headliner

[overZealous1]

a quick wipe down with some alcohol or something isn't a bad idea, but adding heat will go a long ways. if it's in the budget, you really want to do the floor twice.

[1970 TT Rustang]

Ok will do i was thinking alcohol and heat. Thanks for your help mate!!