Sound deadening on the cheap!

https://www.amazon.co.uk/Bond-Flashing-Tape-225mm-10Metres/dp/B0057FU69I/ref=asc_df_B0057FU69I?mcid=705e1e13a54d38439eba36997cef9ec5&tag=googshopuk-21&linkCode=df0&hvadid=697313183651&hvpos=&hvnetw=g&hvrand=6121744564645961281&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9212541&hvtargid=pla-740920208825&psc=1&gad_source=1 I haven't used it on a car but have used a similar product to repair corrugated metal roofs, providing the surface is clean it will last for decades. What I used had a  thin aluminium foil to reflect the heat of the sun. There is absolutely no reason that due to being thicker than Dynamatt it will not be equal or even better at damping panel vibrations. 
 

I have used that aluminium backed tape but on a flat roof!
I actually looked for thst but this came up locally at Screwfix.
As you say it is the vibrations that set up a resonant frequency that pass through the car. 
This stuff tames that and I'm sure anything similar will do the same.
I really hope someone else tries it and reports back!
 

For anyone who has not yet had to remove their door card.

Almost every car I know has a square mat stuck on the door panel to deaden the panel. It can be very thin but either way it helps cut vibrations.
The TF has no such mat. It is quite a long panel and as such has quite a large surface area.
That's why this tape  or other means, has such an effect on the car. It may have zero effect on a Golf.
By removing the speaker you can gain access to half the door with a bit of a wiggle and the other half by the aperture.

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A hairdryer makes it really stick. A heatgun is too much especially around wiring!
 

You have the wrong heat gun, the best type has a variable temp control that lets you dial up (or down) to the required temp, mine goes from 70C to 600C
It's wasn't expensive as it's not even a good one, just some crap private label brand of the store.
The only reason I bought that one was I needed it in a hurry and they didn't have the good brands in stock, it came with a shit load of attachments which are useless as they don't fit properly but I've had it for years and it's never let me down. The gun itself is quite good, though a Bosch Professional (blue) one would be better.

Pro tip. some Power tool brands like Bosch have different levels of product, In the case of Bosch the green tools are cheap handyman rubbish at premium prices but the blue Professional range are very very good, they are built to last have good balance and controls, you can actually feel the difference when you use them. which is why most of my stuff is Bosch blue or Hilti (hideously expensive but absolutely brilliant), with a smattering of Metabo and some old Japanese made Makita, The old Japanese made Makita last forever and are unbreakable, the modern Makita stuff (Mostly made in China or some such) is OK but not the same quality as the old.
Oh and there are some Aldi rubbish battery tools kept in the Ute at all times in case of emergency, in there are an angle grinder, a drill, a small impact driver and a !/2" drive rattle gun (i don't really care much if they get wet, damaged or stolen)
 

My heatgun is shit! How did you know? Even from over there you knew..I'm impressed...mind blown.
It actually is..a Low and High switch meaning Burnt to Incinerate. Tbh I hardly ever need one.
The hairdryer felt safer poking it inside the holes where wiring is abundant and if it will burn you can bet I will burn it.
It's cold over here now and 20 seconds just softened the bitumen enoigh to mould it and really stick.
I have some great tools and some cheapo's that were probably only bought expecting one useage but if they made two I got lucky!

 

Well it survived a very heavy frost. Phew!

Due to having a MGB that I am restoring I go onto this forum on a regular basis; https://www.mgexp.com/forum/mgb-and-gt-forum.1/   There are regular discussions about both heat and sound insulation, the heat insulation is not really relevant but the sound proofing is. The camp is divided in two groups, one say's that Dynamat is the ultimate product and nothing can better it. The other group say that Dynamat is nothing special just clever marketing, they use other butyl rubber pads that are slightly thicker and a lot of others use bitumen based products like the Bostick one. Back in the day MG themselves used bitumen based pads, my GT has them on the door skins and they are still intact forty six years later. I personally think that the push to butyl rubber is due to environmental concerns rather than it being a superior product.
These are still available to dampen vibration and to level the floor in MGB's 
Floor Sound Proofing / Deadening Kit For MGB & MGC 1968 onwards BMH9500 Buy It Now
Incidentally the product that I linked to is available in widths up to a metre wide

If you had a half decent heat gun you would find that you'd probably use it more often,
I last used mine to soften the mastic sealant that secures the water sheader plastic sheet behind the fuel tank panel, the old mastic had stuck to the sheet when I peeled away from the car, so all I had to do to reuse it was press it back with my thumb as I gently heated it....stuck back on like it had never been off!
Heat shrink tubing is your friend when working on automotive electrics, especially it you do it properly and use solder on your terminals instead of those worthless red blue and yellow crimp shit! A good heat gun is the best way to shrink the tubing gently. I eve use it to soften rubber hoses that I would otherwise struggle to fit over the barbed spigot

When softening hoses I usually stick the end to be connected in my wife’s brew whilst it’s still hot.
This is especially useful if it’s really cold, as I can be sure of at least one hot ear, possibly two if I’m not quick enough.
Whenever I’m doing any sort of electrical or electronic work, my heat gun shares the same importance as my soldering equipment.
It’s also great for blowing up the fire when the weather conditions aren’t favourable.
I don’t mind crimp connectors but with the proviso that they are of good quality & the correct tool is used. Cheap crimps create completely crappy connections. Correct?
M

Ok..ok..you are both ganging up on me...I may or may not invest in one but there is always just something else...
I solder a lot with guitar electronics and use heat shrink tubing..my soldering is good..just saying..wink.

C'mon you know we're right!

   I know...