I've used Dynamat and it works very well.
I also have used the 'bubble wrap' insulation on my last TR3 plus on the inside of my old Ford E350 cargo van. The bubble wrap is very inexpensive but it doesn't apply as nicely as Dynamat. It does, however, really reduce the amount of heat transfer to the footwells on a TR3.
I will use Dynamat on TS1203LO this spring. IT's really much easier to work with and the results are pretty professional looking.
On the floor carpeting I'll apply it to the carpet rather than stick it to the steel floor. That way I can remove the inevitable wet carpet and and allow the floors to dry completely.
FWIW...My friend, who does some high-dollar hot rod upholstery jobs, has also graduated from bubble-wrap insulation to Dynamat...for the same reasons.